c programming language

C Programming Language

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History of ‘C’ALGOL International Group

BCPL

B

Traditional C

K & R C

ANSI C

ANSI / ISO C

Martin Richards

Ken Thompson

Dennits Ritchie

Kernighan and Ritchie

ANSI Committee

ISO Committee

1960

1967

1970

1972

1978

1989

1990

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TYPES OF ‘C’ COMPILER

1. Borland ‘C’ Compiler

2. Turbo ‘C’ Compiler

3. Microsoft ‘C’ Compiler

4. ANSI ‘C’ Compiler

Why are using ‘C’• It is a Structured Programming Language• High – Level Language• Machine Independent Language• It allows software developers to develop programs

without worrying about the hardware platforms where they will be implemented

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Characteristics of C We briefly list some of C's characteristics that define the language Small size Extensive use of function calls Loose typing -- unlike PASCAL Structured language Low level (Bitwise) programming readily available Pointer implementation - extensive use of pointers for memory, array,

structures and functions.

C has now become a widely used professional language for various reasons.

• It has high-level constructs. • It can handle low-level activities. • It produces efficient programs. • It can be compiled on a variety of computers.

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Steps in Learning C

Character set

Constants, variableAnd Data types

Control statements

Functions

Files

Structures and Unions

Pointers

Arrays

Data Structures

Algorithms

Programs

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C’S Program StructureDocumentation section

Preprocessor section

Definition section

Global declaration sectionmain() { Declaration part; Executable part;}

Sub program section{

Body of the subprogram}

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C’s Character setC Character set

Source Character set

Execution Character set

AlphabetsA to Z & a to z

Escape Sequences\a,\b,\t,\n

Digits0 to 9

Special Characters+,-,<,>,@,&,$,#,!

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C TOKENS

C TOKENS

Keywords

Identifiers

Strings

Special Symbols

Constants

Operators

-15.5

100

main

amount

float

while

“ABC”

“YEAR”

+ - * /

[ ]

{ }

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C’s Identifiers Program elements where Identifiers are used

VariablesFunctionsArraysFunction parametersMacros and macro parametersType definitions

Rules for Using Identifiers

Only Letter, Digits and Underscore(_) 1st character should be letter or _ Both Upper/lower case can be used It can be of any length No space and Special symbol is used It cant be a keyword

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C’s keyword Basic Building Block of the Program These are the Reserved words These word’s cant be changed

C keywords

autobreakcasecharconstcontinuedefaultdo

doubleelseenumexternfloatforgotoif

intlongregisterreturnshortsignedsizeofstatic

structswitchtypedefunionunsignedvoidvolatilewhile

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Data Types This are the type of the data that are going to access within the

program.

C’s Data Type

Primary User defined Derived EmptyCharIntFloatDouble

typedefArraysPointersStructuresUnion

Void

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C’s Data types cont.

Integer

Signed

Unsigned

Int (%d)2 bytes,-32768 to 32767

Short int (%d)1 bytes, -128 to 127

Long int (%ld)4 bytes,

-2,147,483,648 to 2,147,483,647

Unsigned Int (%d)2 bytes, 0 TO 65, 535

Unsigned shot int (%d)1 bytes, 0 TO 255

Unsigned Long int (%ld)4 bytes,

0 TO 4,294,967,295

The primary data types are further classified as below.Integers are the whole numbers, both positive and negative.

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Float Type

Float (%f or %g)4 bytes, 3.4E -38 to 3.4E +38

Double (%lf)8 bytes, 1.7E -308 to 1.7E +308

Long Double (%lf)10 bytes, 3.4E -4932 to 1.1E+4932

Float are the numbers which contain fractional parts, both Positive and Negative.

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Character Type

Char (%c)1 bytes, -128 to 127

Signed Char (%c)1 bytes, -128 to 127

Unsigned Char (%c)1 bytes, 0 to 255

Char are the characters which contain alpha-numeric character. Characters are usually stored in 8 bits (one byte) of internal storage

The void is the Null Data type.

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C’s Variables

• A variable is a data name as well as identifier that may be used to store a data value.

Rules for Naming the Variablesa) A variable can be of any combination of alphabets, digits and

underscore.b) The first character of the variable can’t be digits.c) The length of the variable can’t be exceeded by 8.(ANSI C – 32

Character)d) No commas, blanks or special symbol are allowed within a variable

name.e) Uppercase and lowercase are significant. That is, the variable Total is

not the same as total or TOTAL.f) It should not be a keyword.g) White space is not allowed.

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C’s Variables cont.Variable Declaration

It tells the computer what the variable name and type of the data

Syntax data_type a1,a2,a3……..an;

Description data_type is the type of the data.a1,a2,a3……an are the list of variables

Example int number;char alpha;float price;

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C’s Variables cont.Initializing Variables

Initialization of variables can be done using assignment operator(=)

Syntax a1 = c1 ;(or) data_type a1 = c1;

Description a1 is the variablec1 is the constantdata_type is the type of the data

Example int a1 = 29;float f1 = 34.45;char c1 = ‘d’

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C’s constant

C constant

Numeric constant

Character constant

Integer constanteg: roll_number = 12345;

Real constanteg: pi = 3.14;

Single Character constanteg: ch = ‘c’; ch = ‘3’;

String constanteg: name = “palani”

The item whose values can’t be changed during execution of program are called constants

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C’s constant Conti…Integer constant

eg: roll_number = 12345;

Hexadecimal constantEg. 0x23

Octal constantEg. 043

Decimal ConstantEg. 35

Real Constanteg: pi = 3.14;

Double Precision ConstantSingle Precision Constant

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Rules for constructing Integer constants

1. An integer constant may be positive or negative (Default sign is

positive).

2. An integer constant should not have a decimal point.

3. No commas and blank spaces are allowed in an integer constant.

4. An integer constant, should not use exponent e.

The suffix u or U is used for denoting unsigned int constants, I or L is used for denoting long int constants, and s is used for denoting short

int constants.

Positive integer Constants 123 4000 +7257

Negative integer Constants -78 -9876 -23

Unsigned integer Constants 1234u 5678u 21057u

Short integer Constants -5008s -23s 1234s

Long integer Constant -40880211 0210578L 0x52123L

Unsigned short integer Constants 1234us 5008us 8476us

Unsigned long integer Constants 1234567890ul

9876543210ul

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Real Constants are often called as Floating – point constants. Real constants is classified as two types.

1. Fractional form.

2. Exponential form.

Rules for constructing real constants (fractional form)

1. A real constant may be positive or negative (Default sign in

positive

2. A real constant must have a decimal point.

3. No commas and blank spaces are allowed in a real constant.

Example:

0.0001 -0.963 485.98+123.456

727.01 0.987 -.8765+001.05

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Rules for constructing Real Constants (Exponential Form)1. The mantissa part and the exponential part should be separated by a letter e.2. The mantissa part and the exponential part may be positive or

negative (Default sign is positive)3. The mantissa and the exponent part must have at least one digit.4. No commas and blank spaces are allowed in a real constant.

Example:+3.2e+5 3.4e5 -8.2e-5-10.9e5 9.7e-10 0.0025e8

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Rules for constructing String Constants

1. A string constant may be a single alphabet or a digit, or a special

character or sequence of alphabets or digits enclosed in double

quotes.

2. Every string constant ends up with a NULL character, which is

automatically assigned.

Example:

“w” “100” “Madhu” “ABC 123”

“Good_Morning” “s1000” “219.71”

“30-01-1978”

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C’ Delimiters

Symbol Name Meaning# Hash Pre-processor directive

, comma Variable delimiters (to separate list of variables)

: colon Label delimiters

; Semi colon Statement delimiters

() parenthesis Used in expressions or in functions

{} Curly braces Used in blocking ‘C’ structure

[] Square braces Used along with arrays

Delimiters are the symbols, which has some syntactic meaning and has got significance.

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C’ Statements

Statements

Expression Statement Compound Statement Control Statement

Statement can be defined as set of declarations (or) sequence of actionAll statements in ‘C’ ends with semicolon(;) except condition and control statement

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C’ Statements

Statements

Assignment statementname = “palani”;

number = 12;

Sex = ‘m’;

Null statement

;

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Expression Statement

1. An Expression is a combination of constant, variables, operators, and function calls written in any form as per the syntax of the C language.

2. The values evaluated in these expressions can be stored in variables and used as a part for evaluating larger expressions.

3. They are evaluated using an assignment statement of the form.

variable = expression;

4. For Example,

age = 21;

result = pow(2,2);

simple_interest = (p * n * r) / 100;

Algebraic Expression Equivalent C Expression

(mnp + qr – at) (m*n* p+q*r-s*t)

(a+b+c) (x+y+z) (a+b+c)*(x+y+z)

abc / x+y (a*b*c) / (x+y)

8a3 + 3a2 + 2a 8*a*a*a+3*a*a+2*a

(a-b)+(x-y) / mn ((a-b)+(x-y)) / (m*n)

8.8(a+b-c) + c / pq 8.8 * (a+b-c) + (c / (p*q))

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Compound Statements 1. A group of valid C expression statements placed within an opening flower brace ‘{‘ and

closing flower brace ‘}’ is referred as a Compound Statements.2. For Example,

{X = (A + (B * 3) – C);Y = A + B * 3;Z = A * (B * 3 – C);

}

1. This statement normally executed sequentially as they appear in the program. 2. In some situations where we may have to change the order of execution of statements until

some specified conditions are met.3. The control statement alter the execution of statements depending upon the conditions specified inside the parenthesis.4. For Example,

if (a == b) if ((x < y) && (y > z)){ { -------- ----------- -------- -----------} }

Control Statements

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Constant Meaning‘\a’ Audible alert (bell)

‘\b’ Back space

‘\f’ Form feed

‘\n’ New line

‘\r’ Carriage return

‘\t’ Horizontal tab

‘\v’ Vertical tab

‘\’’ Single quote

‘\”’ Double quote

‘\?’ Question mark

‘\\’ Backslash

‘\0’ Null

ESCAPE SEQUENTIAL CHARACTER OR BACKSLASH CHARACTER CONSTANTS

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Operators An operator is a symbol that specifies an operation to be performed

on the operands

Some operator needs two operands (binary) Eg: a+b; ‘+’ is an operator and ‘a’ and ‘b’ are the operands Some operator needs one operand (unary) Eg: ++a;

‘++’ is an operator and a is the operand

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Types of Operatorsoperators

Arithmetic operator

Relational operators

Logical operator

Assignment operator

Increment and Decrement Operator (Unary Op.)

Conditional operator (Ternary operator)

Bitwise operator

Special operator

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Arithmetic Operators

Operator Meaning Examples+ Addition 1+2 = 3

- Subtraction 3 -2 = 1

* Multiplication 2*2 = 4

/ Division 2/2 = 1

% Modulo division 10/3= 1

This operators help us to carryout basic arithmetic operations such addition, subtraction, multiplication, division

Operation Result Examples

Int/int int 2/2 = 1

Real/int real 7.0/2 = 3.5

Int/real real 7/2.0 = 3.5

Real/real real 7.0/2.0 = 3.5

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Relational Operator• This are used to compare two or more operands.• Operands can be variables, constants or expression.• eg: comparison of two marks or two values.

Operator Meaning Example Return value

< is less than 5<6 1

<= is less than or equal to 4<=4 1

> is greater than 5>7 0

>= is greater than or equal to 7>=5 0

== equal to 6==6 1

!= not equal to 5!=5 0

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Logical Operator

Operator Meaning Example Return value

&& Logical And (9>2) && (6>4) 1

|| Logical OR (9>2) || (3.4) 1

! Logical Not 4 ! 4 0

AND truth tableTrue True True

True False False

False True False

False False False

OR truth tableTrue True True

True False True

False True True

False False False

• This operators are used to combine the results of two or more conditions.

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Assignment Operator This are used to assign a value or an expression or a variable to another variable eg: a = 10; n1 = 20;

Syntax:

identifier = expression;

a) Compound Assignment This operator are used to assign a value to a variable in order to assign a new

value to a variable after performing a specified operation. eg: a+=10,n1-=20;b) Nested Assignment (Multiple)

This operator are used to assign a single value to multiple variables eg: a=b=c=d=e=10;

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List of Shorthand or Compound Assignment Operator

Operator Meaning+= Assign Sum

-= Assign Difference

*= Assign Product

/= Assign Quotient

%= Assign Remainder

~= Assign One’s Complement

<<= Assign Left Shift

>>= Assign Right Shift

&= Assign Bitwise AND

!= Assign Bitwise OR

^= Assign Bitwise X - OR

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Increment and Decrement operator

• C provide two operator for incrementing a value or decrementing a value

a) ++ Increment operator (adds one to the variable) b) -- Decrement operator (Minus one to the variable) eg: a++ (if a= 10 then the output would be 11)

Operator Meaning

++X Pre increment

X++ Post increment

--X Pre decrement

X-- Post decrement

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Increment and Decrement operator Conti…

Expression Result+ + X 4

X + + 3

- - X 2

X - - 3

If the value of the operand x is 3 then the various expressions and their results are

The pre – increment operation (++X) increments x by 1 and then assign the value to x. The post – increment operation (X++) assigns the value to x and then increments 1. The pre-decrement operation ( --X) decrements 1 and then assigns to x. The post – decrement operation (x--) assigns the value to x and then decrements 1. These operators are usually very efficient, but causes confusion if your try to use too many evaluations in a single statement.

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Conditional Operator

• It is used check the condition and execute the statement depending upon the condition

Syntax Condition?exp1:exp2Description The ‘?’ operator act as ternary

operator, it first evaluate the condition, if it is true then exp1 is evaluated if the condition is false then exp2 is evaluated

Example a= 2; b=3ans = a>b?a:b;printf (ans);

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Bitwise Operator• This are used to manipulate the data at bit level• It operates only on integers

Operator Meaning

& Bitwise AND

| Bitwise OR

^ Bitwise XOR

<< Shift left

>> Shift right

~ One’s complement

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Bitwise Operator cont.

Bitwise AND (both the operand should be high for 1)

0 0 0

1 1 1

Bitwise XOR (the two operands should be different for 1)

0 0 1

1 1 0

• The truth table for Bitwise AND,OR and XOR

Bitwise OR (either of the operand should be high for 1)

0 0 0

1 1 1

Eg: x = 3 = 0000 0011 y = 4 = 0000 0100

x&y = 0000 0000

Eg: x = 3 = 0000 0011 y = 4 = 0000 0100

x|y = 0000 0111

Eg: x = 3 = 0000 0011 y = 4 = 0000 0100

x ^ y = 0000 0111

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Bitwise Operator cont.Bitwise One’s Complement

The one’s complement operator (~) is a unary operator, which causes the bits of the operand to be inverted (i.e., one’s becomes zero’s and zero’s become one’s)

For Example, if x = 7

i.e 8 – bit binary digit is 0 0 0 0 0 1 1 1

The One’s Complement is 1 1 1 1 1 0 0 0

Bitwise Left Shift OperatorThe Left shift operator (<<) shifts each bit of the operand to its Left. The general form or

the syntax of Left shift operator is

variable << no. of bits positions

if x = 7 (i.e., 0 0 0 0 0 1 1 1) the value of y in the expression

y = x <<1 is 14

0 0 0 0 1 1 1 0 = 14 since it shifts the bit position to its left by one bit. The value stored in x is multiplied by 2N (where n is the no of bit positions) to get the required value. For example, if x = 7 the result of the expression y = x << 2 is y = x * 22 (i.e. 28)

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Bitwise Operator cont.Bitwise Right Shift Operator

The Right shift operator (>>) shifts each bit of the operand to its Right. The general form or the syntax of Right shift operator is

variable >> no. of bits positions

if x = 7 (i.e., 0 0 0 0 0 1 1 1) the value of y in the expression

y = x >> 1 is 3

0 0 0 0 0 0 1 1 = 3 since it shifts the bit position to its right by one bit. The value stored in x is divided by 2N (where n is the no of bit positions) to get the required value. For example, if x = 7 the result of the expression y = x << 2 is y = x / 22 (i.e. 1). If you use the left shift operator i.e. x = x << 1 the value of x will be equal to 2 (i.e., 0 0 0 0 0 0 1 0) since the lost bit cannot be taken back.

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Some of the special operators used in C language. These operators are referred as separators or punctuators.

1. Ampersand (&) 2. Comma (,)

3. Asterisk ( * ) 4. Ellipsis (…)

5. Braces ({}) 6. Hash (#)

7. Brackets ([]) 8. Parenthesis (())

9. Colon (:) 10. Semicolon(;)

Special Operator

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Special OperatorOperator Meaning

Ampersand(&)

Ampersand (&) also referred as address operator usually precedes the identifier name, which indicates the memory location (Address) of the identifier.

Asterisk( * )

Asterisk ( * ) also referred as an indirection operator, is an unary operatorusally precedes the identifier name, which indicates the creation of apointer operator.

Braces( {} )

The opening ( { ) and closing ( } ) braces indicate the start and end of compound statement or a function. A semicolon is not necessary after the closing brace of the statement, except in case of structure declaration.

Brackets( [ ] )

Brackets [ ] also referred as array subscript operator is used to indicate single and multi dimensional array subscripts.

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Colon ( : ) Colon ( : ) is used in labels.

Comma ( , ) Comma ( , ) operator is used to link the related expressions together. Comma used expressions are linked from left to right and the value of the right most expression is the value of the combined expression. The comma operator has the lowest precedence of all operators.For Example: sum = (x = 5, y = 3, x + y); The result will be sum = 8

Ellipsis (. . .) Ellipsis (…) are three successive periods with no white space in between them. It is used in function prototypes to indicate that this function can have any number of arguments with varying types.For Example: void fun(char cName, int iAge, float fSalary, . . .); The above declaration indicates that fun () is a function that takes at least three arguments, a char, an int and a float in the order specified but can have any number of additional arguments of any type.

Hash ( # ) Hash ( # ) also referred as pound sign is used to indicate preprocessor directives.

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Parenthesis( () )

Parenthesis ( ) also referred as function call operator is used to indicate the opening and closing of function prototypes, function calls, function parameters, etc., Parenthesis are also used to group expressions, and there by changing the order of evaluation of expressions.

Semicolon ( ; ) Semicolon ( ; ) is a statement terminator. It is used to end a C statement. All valid C statements must end with a semicolon. Which the C compiler interprets as the end of the statement.

Sizeof ( ) The sizeof operator is not a library function but a keyword, which returns the size of the operand in bytes. The sizeof operator always, precedes its operand. This operator can be used for dynamic memory allocation.Example: 1. sizeof(char) = 1 2. sizeof(int) = 2 3. sizeof(float) = 4 4. sizeof(doubles) = 8

Operator Precedence and Associativity of Operator

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1. Each operator in C has a precedence associated with it.

2. This precedence is used to determine how an expression involving more than one operator is evaluated.

3. These are distinct levels of precedence and an operator may belong to one of these levels.

4. The operators at the higher level of precedence are evaluated first.

5. The operators of the same precedence are evaluated either from ‘left to right’ or from ‘right to left’, depending on the level.

6. That is known as the associativity property of an operator.

What is Precedence Rule and Associative Rule

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Arithmetic operators precedence

• The precedence of an operator gives the order in which operators are applied in expressions: the highest precedence operator is applied

first, followed by the next highest, and so on. • eg: Arithmetic operator precedence

Precedence operatorHigh *,/,%Low +,-

The arithmetic expression evaluation is carried out using two phases from left to right through the expressions

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Example:if (x == 10 +15 && y <10)

The precedence rules say that the addition operator has a higher priority than the logical operator (&&) and the relational operators (== and <). Therefore, the addition of 10 and 15 is executed first. This is equivalent to: if (x == 25 && y < 10)

The next step is to determine whether x is equal to 25 and y is less than 10, if we assume a value of 20 for x and 5 for y, then

x == 25 is FALSE (0)y <10 is TRUE (1)

Note that since the operator < enjoys a higher priority compared to ==, y < 10 is tested first and then x ==25 is tested.

Finally we get,

if (FALSE && TRUE)

Because one of the conditions is FALSE, the complex condition is FALSE.

In the case of &&, it is guaranteed that the second operand will not be evaluated if the first is zero and in the case of || , the second operand will not be evaluated if the first is non – zero.

Relational operators precedence

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Precedence and Associativity Table

• The following table lists all the operators, in order of precedence, with their associativity

Operators Operations Associativity priority() Function call Left to Right 1

[] Square brackets

-> Structure operator

. Dot operator

+ Unary plus Right to Left 2

- Unary minus

++ Increment

-- Decrement

! Not

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Precedence and Associativity Table cont.

Operators Operations Associativity priority

~ Complement Right to Left 2

* Pointer operation

& Address operator

Sizeof Size of operator

type Type cast

* Multiplication Left to Right 3

/ Division

% Modulo

+ Addition Left to Right 4

- Subtraction

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Operators Operations Associativity priority<< Left shift Left to Right

Left to Right

5

6>> Right shift

< is less than

<= is less than or equal to

> is greater than

>= is greater than or equal to

== equal to

!= not equal to

& Bitwise AND Left to Right 7

| Bitwise OR

^ Bitwise XOR

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Operators Operations Associativity priority&& Logical And Left to Right 8

|| Logical OR

?= Conditional Right to Left 9

=,*=,-=,&=,+=,^=,!=,<<=,>>=

Assignment Right to Left 10

, comma Left to Right 11

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Rules for evaluation of expression• Evaluate the sub expression from left to right if parenthesized.• Evaluate the arithmetic expression from left to right using the rules of

precedence.• The highest precedence is given to the expressions with in

parenthesis.• Apply the associative rule if more operators of the same precedence

occurs.• Evaluate the inner most sub expression if the parenthesis are nested.

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Sample Expression

• Exp = a - 2 * a * b + b / 4

Let us have a=10,b=20

exp = 10 - 2 * 10 * 20 + 20 / 4

Phase I exp = 2*10*20 , 20/4 will be evaluated. phase II exp = 10-400+5 will be evaluated. Result exp = -395.

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Expression Evaluation

Let us see some examples for evaluating expression.

Let a = 5, b = 8, c = 2.

x = b / c + a * c

4 10

14

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Let us see some examples for evaluating expression.

Let a = 5, b = 8, c = 2.

y = a + (b * 3) - c

29

27

24

Expression Evaluation

TYPE CONVERSION

OR

TYPE CASTING

What is Type Conversion or Type Casting

Type Casting means One data type converted into another data type. This is called Type conversion or Type casting.

Example:

1. Integer into floating point number

2. Character into integer

3. Floating point number into Integer Number

Type conversion is classified into two types.

1. Implicit Type Conversion (Automatic Type Conversion)

2. Explicit Type Conversion (Manual Type Conversion)

Type Conversion

Implicit Conversion

Explicit Conversion

Automatic Conversion

Casting Operation

Type Conversion Hierarchy

short char

int

unsigned int

long int

unsigned long int

float

double

long double

Implicit Type

Conversion

Explicit Type

Conversion

Implicit Type Conversion

1. The Implicit Type Conversion is known as Automatic Type Conversion.

2. C automatically converts any intermediate values to the proper type so that the expression can be evaluated without loosing any significance.

3. Implicit type Conversion also known as Converted Lower order data type into Higher order data type.

4. Implicit Type Conversion also known as Widening.

Example:

int a, b;

float c;

c = a + b;

Print c;

float a,b;

int c;

c = a + b; // This is Wrong

Print c;

Explicit Type Conversion

1. The Explicit Type Conversion is, there are instances when we want to force a type conversion in a way that is different from the automatic conversion.

2. The Explicit Type Conversion is Converted Higher order data type into Lower order data type.

3. The Explicit type Conversion is also known as borrowing.

4. The Explicit type conversion forces by a casting operator.

Disadvantage of Explicit Type Conversion

1. float to int causes truncation of the fractional part.

2. double to float causes rounding of digits.

3. Long int to int causes dropping of the excess higher order bits.

The general form of the casting is

(type_name) expression;

Where type_name is one of the standard C data type.

The expression may be a constant, variables or an expression.

For Example:

float a, b;

int c;

c = (int) a + (int) b;

Print c;

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Use of Casts

Example Action

x = (int) 7.5 7.5 is converted to integer by truncation.

a = (int) 21.3 / (int) 4.5 Evaluated as 21 / 4 and the result would be 5.

b = (double) sum / n Division is done in floating point mode.

y = (int) (a + b) The result of a + b is converted to integer.

z = (int) a + b a is converted to integer and then added to b.

p = cos ((double) x) Converts x to double before using it.

Input And Output Functions

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Ip / Op Statements

We have two methods for providing data to the program.

a) Assigning the data to the variables in a program. b) By using the input/output statements.

‘c’ language supports two types of Ip / Op statements This operations are carried out through function calls. Those function are collectively known as standard I / O library

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Ip / Op Statements cont.

Ip / Op Functions

Unformatted Ip / Op statementsInput Outputgetc() putc()getch() putch()Gets() puts()

Formatted Ip / Op statements

Input OutputScanf() printf()fscanf() fprintf()

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Unformatted Ip / Op statements

getch() function

Syntax char variable = getch();

Description char is the data type of the variable;getch() is the function

Example char x = getch();putch (x);

• These statements are used to input / output a single / group of characters from / to the input / output device.

Single character Input/output function

putch() function

Syntax putch (character variable);

Description char variable is the valid ‘c’ variable of the type of char data type.

Example char x ;putch (x);

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Unformatted Ip / Op statements cont.

gets() functionSyntax gets (char type of array

variable);

Description valid ‘c’ variable declared as one dimensional array.

Example char s[10];gets (s);

Group of character Input / output function. Gets() and puts are used to read / display the string from / to the

standard input / output device.

puts() function

Syntax puts (char type of array variable)

Description valid ‘c’ variable declared as one dimensional array.

Example char s[10];gets (s);puts (s);

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Sample Program#include<stdio.h>Void main(){ char name[10]; char address[20]; Puts(“Enter the name : ”); gets(name); puts(“Enter the address : ”); gets(address); puts(“Name = “) puts(name); puts(“Address = “); puts(address);}

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Formatted Ip / Op statements It refers to Input / Output that has been arranged in a particular format. Using this statements, the user must specify the type of data, that is going to

be accessed.

scanf() (This function is used to enter any combination of input).

Syntax scanf (“control strings”,var1,var2…..var n);

Description control strings is the type of data that user going to access via the input statements.var1,var2 are the variables in which the data’s are stored.

Example int n;scanf (“%d”, &n);

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Formatted Ip / Op statements Control strings i) It is the type of data that user is going to access via the input statement ii) These can be formatted . iii) Always preceded with a ‘%’ symbol.

Format code Variable type Display

%c Char Single character

%d Int Decimal integer -32768 to 32768

%s Array of char Print a Strings

%f Float or double Float point value without exponent

%ld Long int Long integer -65536 to 65535

%u Int Unsigned decimal integer

%o Int Octal integer number without leading zero

%x Int Hexadecimal integer number without leading 0x

%e Float or double Float point values in exponent form

%h int Short integer

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Rules for scanf() The control strings must be preceded with ‘%’ sign and must be within quotations. If there is a number of input data items, items should be separated by commas and

must be preceded with ‘&’ sign except for char data types. The control strings and the variables going to input should match with each other. It must have termination. The scanf() reads the data values until the blank space in numeric input.

Apart from ‘%’ it can have ‘*’ sign. This is used to ignore the values inputted.

eg: scanf(“%d%d%*d%*d%d”,&I,&j,&k);

if the input is 10 20 3040 50 The output will be i = 10, j = 20, k = 50;

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Printf()

printf() (This function is used to display the result or the output data on to screen)

Syntax printf (“control strings”,var1,var2…..var n);

Description Control strings can be anyone of the followinga) Format code character codeb) Execution character setc) Character/strings to be displayedVar1,var2 are the variables in which the data’s are stored.

Example printf (“this is computer fundamental class”);printf (“/n computer fundamental class”);

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Rules for printf()

variables should be separated by commas and need not be preceded with ‘&’ sign.

The control strings and the variables must match with each other.

The control string must be in quotations and there we can also use any other text to print with data.

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Formatted IO / OP

• Writing integers numbers

Syntax Printf (%w.pd”,var1)Description W is used to specify the minimum field width for the

output.P is the precession value.D is the control string specification

Example Printf ( “%5.4d”,23);The output will be $0023.Printf (“%05d”,23);The output will be 00023.

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Formatted IO / OP

• Writing Real Numbers

Syntax Printf (%w.p.f”,var1)Description W is used to specify the minimum field width for the

output.P is the number of digits to be displayed after the decimal point.f is the control string for float.

Example Printf ( “%5.2.f”,2345.567890);The output will be $2345.56.Printf (“%10.2e”,48.3333);The output will be 4.8e+01

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Sample Programinclude<stdio.h>include<conio.h>void main(){int r,t;char u,y;float a,b,c,d;clrscr();scanf("%d%d",&r,&t);printf("enter the char value");scanf("%c",&y);printf("\n%9c%9c",r,t);printf("\n\t%d\t\%d",r,t);printf("\n the value of u is %c",y);getch();}

Control Statements(Decision Making)

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Control Statements

A program consists of a number of statements which are usually executed in sequence. Programs can be much more powerful if we can control the order in which statements are run.

Statements fall into three general types;

1) Assignment, where values, usually the results of calculations, are stored in variables.

2) Input / Output, data is read in or printed out. 3) Control, the program makes a decision about what to do next.

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Control Statements

Control statements in C are used to write powerful programs by;

Repeating important sections of the program. Selecting between optional sections of a program.

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Control StatementsControl statements

Selection Statements Iteration statements

The if else statement

The switch statements

The while loop &Do while loop

The for loop

The break statement

Continue statement

Goto statement

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Control Statements cont.• ‘C’ language provides four general structure by which statements can

be executed

Structure Meaning Example

Sequential It means the instructions are carried out in sequence

a+=5;a=a+b;

Selection Sequence of the instruction are determined by the result of the condition

if (x>y) a = a+1;else a= a-1;

Iteration Here the statements are repeatedly executed

while (a<=10)printf (“%d” , a);

Encapsulation Here the an iteration statement can have selection inside it or vice versa

while (a<=10) { if(a>5) printf (%d” , a);}

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SELECTION STATEMENT

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Types of Selection Statement

1. Simple if Selection statement

2. if else Selection statement

3. Nested if else Selection statement

4. else if ladder Selection statement

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Simple if Selection statement

It is used to control the flow of execution of the statements and also to test logically whether the condition is true or false.

if the condition is true then the statement following the “if “ is executed ifit is false then the statement is skipped.

Syntax: if ( condition ) { statement ; }

Test Condition

Executable X - Statement

True

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Selection Statement

• Properties of an if statement

a) if the condition is true then the simple or compound statements are executed.

b) If the condition is false it will skip the statement.c) The condition is given in parenthesis and must be evaluated

as true or false.d) If a compound structure is provided, it must be enclosed in

opening and closing braces

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//Biggest of Two Numbers

#include <stdio.h>

void main()

{

int a, b;

clrscr();

printf(“Enter the A and B Value:\n”);

scanf(“%d”, &a);

if (a > b)

{

printf(“A is Big”);

}

getch();

}

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• Basic Relational Operators can be used in C to make “if” statement conditions more useful

• The 6 Basic Relational Operators are

> , <, >= , <= , == , !=

(greater than, less than, greater than or equal to, less than or equal to, equal to, not equal to)

Basic Relational Operators

Basic Logic Operators• Basic Logic Operators can be used to combine more than one

condition in an “if” statement or invert the result of a condition• The 3 Basic Logic Operators are

&& , || , !

(and, or, not)

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The if else statement It is used to execute some statements when the condition is true and execute some other

statements when the condition is false depending on the logical test.Syntax: if ( condition ) { statement 1 ; (if the condition is true this statement will be executed) } else { statement 2 ; (if the condition is false this statement will be executed) }

Test Condition

Executable X - Statement

True

Executable Y - Statement

False

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if else statements

if (result >= 45){

printf ( “ Passed\n “ ) ; printf ( “ Congratulations\n “ ) }else{

printf ( “ Failed\n “ ) ; printf ( “ Good luck in the resits\n “ ) ; }

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// Biggest of Two Numbers

#include <stdio.h>

void main(){

int a, b;clrscr();

printf(“Enter the A and B Value:\n”);scanf(“%d”, &a);

if (a > b){

printf(“A is Big”);}

else{

printf(“B is Big”);}

getch();}

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// Given Number is ODD or EVEN Number#include <stdio.h>

void main(){

int n;clrscr();

printf(“Enter the Number:\n”);scanf(“%d”, &n);

if (n % 2 == 0){

printf(“Given Number is Even Number”);}else{

printf(“Given Number is Odd Number”);}

getch();}

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Nested if….. else statement

Syntax:

if ( condition 1){

if ( condition 2)statement 1 ;

elsestatement 2 ;

}else{

if (condition 3)statement 3;

elsestatement 4;

}

when a series of if…else statements are occurred in a program, we can write an entire if…else statement in another if…else statement called nesting

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Test Condition_1

Executable X2 - Statement

Test Condition_2

Executable X1 - Statement

Test Condition_3

Executable X4 - Statement Executable X3 - Statement

TRUE

TRUE

TRUE

FALSE

FALSE

FALSE

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// Biggest of Three Numbers

#include<stdio.h>void main(){

int a, b, c;clrscr();

printf(“Enter the Three Numbers:\n”);scanf(“%d%d%d”,&a,&b,&c);

if (a > b){

if (a > c)printf(“A is Big”);

elseprintf(“C is Big”);

}else{

if (b > c)printf(“B is Big”);

elseprintf(“C is Big”);

}getch();

}

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else if Ladder or Multiple if else Statements

Syntax:

if (condition_1)executed statement_1;

else if (condition_2) executed statement_2; else if (condition_3)

executed statement_3;-------------------------------------------- else if (condition_n)

executed statement_n; else

executed statement_x;

When a series of decisions are involved we have to use more than one if – else statement called as multiple if’s. Multiple if – else statements are much faster than a series of if – else statements, since theif structure is exited when any one of the condition is satisfied.

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Test Condition_1

Test Condition_2

Exec. Stat_1

Test Condition_3

TRUE

Test Condition_n

Exec. Stat_2

Exec. Stat_3

Exec. Stat_nExec. Stat_X

TRUE

TRUE

TRUE

FALSE

FALSE

FALSE

FALSE

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else if Ladder

if (result >= 75) printf ( “ Passed: Grade A\n “ ) ;

else if (result >= 60)printf ( “ Passed: Grade B\n “ ) ;

else if (result >= 45) printf ( “ Passed: Grade C\n “ ) ;

elseprintf ( “ Failed\n “ ) ;

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main() { int n1,n2;

int val; char op; printf("Enter a simple expression ");

scanf("%d%c%d",&n1,&op,&n2); if(op == '+') val = n1 + n2; else if(op == '-')

val = n1 - n2; else if(op == '/') val = n1 / n2; else if(op == '*')

val = n1 * n2;

else { printf(“?? operator %c\n",op); exit(1); } printf("%d%c%d = %d\n",n1,op,n2); }

/*This program reads in a simple expression with a very restricted format and prints out its value. */

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Sample Program

• Write a program to calculate the sales commission for the data given below:

Sales value (Rs) Commission(%)

Less than 1000 No commission Above 1000 but below 2000 5% of sales Above 2000 but below 5000 8% of sales Above 5000 10% of sales

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#include<stdio.h>#include<conio.h>Void main(){ float sales, com; printf(“Enter the sales value :”); scanf(“%f”, &sales); if(sales<=1000) com = 0; else if(sales>1000 && sales <=2000) com = sales*5/100; else if(sales>2000 && sales <=5000) com = sales*5/100; else com = sales * 10/100; printf(“The commission for the sales value %f is %f”, sales, com);}

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THE SWITCH STATEMENT

• The control statements which allow us to make a decision from the number of choices is called switch (or) Switch-case statement.

• It is a multi way decision statement, it test the given variable (or) expression against a list of case value.

switch (expression){ case constant 1: simple statement (or) compound statement; case constant 2: simple statement (or) compound statement; case constant 3: simple statement (or) compound statement; }

switch (expression){ case constant 1: simple statement (or) compound statement; case constant 2: simple statement (or) compound statement; default : simple statement (or) compound statement; }

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Example Without Break Statement#include<stdio.h>void main (){

int num1,num2,choice;printf(“Enter the Two Numbers:\n”);scanf(“%d%d”,&num1,&num2);printf(“1 -> Addition\n””);printf(“2->Subtraction\n”);printf(“3->Multiplication\n”);printf(“4->Division\n”);printf(“Enter your Choice:\n”);scanf(“%d”,&choice);

switch(choice){

case 1: Printf(“Sum is %d\n”, num1+num2);

case 2: Printf(“Diif. is %d\n”, num1-num2);

case 3: Printf(“Product is %d\n”,

num1*num2);

case 4: Printf(“Division is %d\n”, num1/num2);

default: printf (“Invalid Choice…..\n”);

}

getch();}

#include<stdio.h>void main (){

int num1,num2,choice;printf(“Enter the Two Numbers:\n”);scanf(“%d%d”,&num1,&num2);printf(“1 -> Addition\n””);printf(“2->Subtraction\n”);printf(“3->Multiplication\n”);printf(“4->Division\n”);printf(“Enter your Choice:\n”);scanf(“%d”,&choice);

switch(choice){

case 1: printf(“Sum is %d\n”, num1+num2); break;case 2:

printf(“Diif. is %d\n”, num1-num2); break;case 3: printf(“Product is %d\n”,

num1*num2); break;case 4:

printf(“Division is %d\n”, num1/num2); break;default: printf (“Invalid Choice…..\n”);

}

getch();}

Example With Break Statement

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Fall through Statement in C

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Rules for Switch

The expression in the switch statement must be an integer or character constant. No real numbers are used in an expression. The default is optional and can be placed anywhere, but usually placed at end. The case keyword must be terminated with colon (:); No two case constant are identical. The values of switch expression is compared with case constant in the order specified i.e

from top to bottom. The compound statements are no need to enclose within pair of braces. Integer Expression used in different case statements can be specified in any order. A switch may occur within another switch, but it is rarely done. Such statements are called

as nested switch statements. The switch statement is very useful while writing menu driven programs.

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Limitations of using a switch statement

Only One variable can be tested with the available case statements with the values stored in them (i.e., you cannot use relational operators and combine two or more conditions as in the case of if or if – else statements).

Floating – point, double, and long type variables cannot be used as cases in the switch statement.

Multiple statements can be executed in each case without the use of pair of braces as in the case of if or if – else statement.

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Iteration Statements1. Iteration statements is also known as Looping statement.2. A segment of the program that is executed repeatedly is called as a loop.3. Some portion of the program has to be specified several number of times or until a

particular condition is satisfied.4. Such repetitive operation is done through a loop structure.5. The Three methods by which you can repeat a part of a program are,

1. while Loops2. do….while loops3. for Loop

Loops generally consist of two parts :

Control expressions: One or more control expressions which control the execution of the loop, Body : which is the statement or set of statements which is executed over

and over

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Any looping statement , would include the following steps:

a) Initialization of a condition variable

b) Test the control statement.

c) Executing the body of the loop depending on the condition.

d) Updating the condition variable.

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While Loop

A while loop has one control expression, and executes as long as that expression is true. The general syntax of a while loop is

A while loop is an entry controlled loop statement.

initialize loop counter;while (condition){

statement (s);increment or decrement loop counter

}

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Start

Initialize

Test Condition

Body of Loop

Increment or Decrement

Stop

False

True

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Example:

// Print the I Values

#include <stdio.h>

void main()

{

int i;

clrscr();

i = 0;

while(i<=10)

{

printf(“The I Value is :%d\n”,i);

++I;

}

getch();

}

// Summation of the series 1 + 2 + 3 + 4 + …….

#include <stdio.h>

void main()

{

int i, sum;

clrscr();

i = 1;

sum = 0;

while(i<=10)

{

sum = sum + i

printf(“The Sum Value is:%d\n”,i);

++I;

}

getch();

}

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Example:

//Summation of the series 12 + 22 + 32 + …..

#include <stdio.h>

#include<math.h>

void main()

{

int i, sum;

clrscr();

i = 1;

sum = 0;

while(i<=10)

{

sum = sum + i*i; //or I ^2 or pow(i, 2)


++I;

}

getch(); }

//Summation of the series 11 + 22 + 33 + …..

#include <stdio.h>

#include<math.h>

void main()

{

int i, sum;

clrscr();

i = 1;

sum = 0;

while(i<=10)

{

sum = sum + pow(i,i)


++I;

}

getch(); }

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#include<stdio.h>void main(){

int number=0, rem=0, sum=0;

clrscr();

printf(“Enter the value for number”);scanf(“%d”,&n);

while(number > 0){

rem = number % 10;sum = sum + rem;number = number / 10;

}

printf(“the summation value of the given number %d is = %d”,number,sum);

}

Wap to print the summation of digits of any given number.

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THE do-while LOOP• The body of the loop may not be executed if the condition is not satisfied in while

loop.• Since the test is done at the end of the loop, the statements in the braces will

always be executed at least once.• The statements in the braces are executed repeatedly as long as the expression

in the parentheses is true.

Make a note that do while ends in a ; (semicolon)Note that Do… While Looping statement is Exit Controlled Looping statement

initialize loop counter;do{

statement (s);increment or decrement loop counter

}while (condition);

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Start

Initialize

Test Condition

Body of Loop

Increment or Decrement

Stop

False

True

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Sl.No. while loop do-while loop

1. The while loop tests the condition beforeeach iteration.

The do – while loop tests the condition afterthe first iteration.

2. If the condition fails initially the loop isSkipped entirely even in the first iteration.

Even if the condition fails initially the loop isexecuted once.

Difference Between While Loop and Do – While Loop

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Example:


#include <stdio.h>

void main()

{

int i;

clrscr();

i = 0;

do

{


++I;

}

while(i<=10);

getch();

}


#include <stdio.h>

void main()

{

int i;

clrscr();

i = 11;

do

{


++I;

}

while(i<=10);

getch();

}

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#include <stdio.h>void main(){

int i, f1,f2,f3;clrscr();f1 = 0;f2 = 1;printf(“The Fibonacci Series is:\n”)printf(“%d\n”,f1);printf(“%d\n”,f2);do{

f3 = f1 + f2;printf(%d\n”,f3);f1 = f2;f2 = f3;

++i;}while(i <= 10);

getch();}

Wap to print the Fibonacci series for any given number Using Do….While Loop

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for LoopThe for loop is another repetitive control structure, and is used to execute set of instruction repeatedly until the condition becomes false.To set up an initial condition and then modify some value to perform each succeeding loop as long as some condition is true.

The syntax of a for loop is

The three expressions : expr1 - sets up the initial condition, expr2 - tests whether another trip through the loop should be taken, expr3 - increments or updates things after each trip.

for( expr1; expr2 ;expr3){ Body of the loop;}

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Start

Initialize; test_condition; Increment / Decrement

Body of Loop

Stop

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Example

#include<stdio.h>

void main()

{

for (int i = 1; i <= 10; i++)

printf("i is %d\n", i);

}

There is no need of { } braces for single line statement and for multiple line it is

essential else it will consider only next line of for statement.

Given example will print the values from 1 to 10.

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Example

#include<stdio.h>#include<conio.h>void main(){

int mul,limit,c,i;clrscr();

printf("Enter the Multiplication Number:\n");scanf("%d",&mul);printf("Enter the Limits:\n");scanf("%d",&limit);

for(i=1;i<=limit;i++){

c = i * mul;printf("%d * %d: %d\n",i,mul,c);

}

getch();}

Given example of Multiplication Table

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Additional Features of for Loop

Case 1:

The statement

p = 1;

for (n = 0; n < 17; ++ n)

can be rewritten as

for (p = 1, n = 0; n < 17;++n)

Case 2:

The second feature is that the test – condition may have any compound relation and

the testing need not be limited only to the loop control variable.

sum = 0;

for (i = 1; i < 20 && sum < 100; ++ i)

{

sum = sum + i;

printf(“%d %d\n”, i, sum);

}

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Additional Features of for Loop Conti…

Case 3:It also permissible to use expressions in the assignment statements of initialization

and increments sections.For Example:

for (x = (m + n) / 2; x > 0; x = x / 2)Case 4:

Another unique aspect of for loop is that one or more sections can be omitted, if necessary.

For Example:m = 5;for ( ; m ! = 100 ;){

printf(“%d\n”,m);m = m + 5;

}Both the initialization and increment sections are omitted in the for statement. The

initialization has been done before the for statement and the control variable is incremented inside the loop. In such cases, the sections are left ‘blank’. However, the semicolons separating the sections must remain. If the test – condition is not present, the for statement sets up an ‘infinite’ loop. Such loops can be broken using break or goto statements in the loop.

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Case 5:We can set up time delay loops using the null statement as follows:

for ( j = 1000; j > 0; j = j – 1)1. This is loop is executed 1000 times without producing any output; it simply causes a

time delay.2. Notice that the body of the loop contains only a semicolon, known as a null statement.

Case 6:for ( j = 1000; j > 0; j = j – 1)

This implies that the C compiler will not give an error message if we place a semicolon by mistake at the end of a for statement. The semicolon will be considered as a null statement and the program may produce some nonsense.

Additional Features of for Loop Conti…

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Nesting of for Loop

The One for statement within another for statement is called Nesting for Loop.

Syntax:

for (initialize; test_condi; incre. / decre.){

------------------------------for (initialize; test_condi; incre. / decre.){

----------------------

}------------------------------

}----------------------------------

Outer for LoopInner for

Loop

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Example

// Print the I and J Value


int I, j;clrscr();

for (i = 1; I < = 10 ; I ++){

printf (“The I Value is %d \n", i);

for (j = 1; j < = 10; j ++){

printf (“The J Value is %d \n", j);

}}

getch();}

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Example

// Multiplication Table


int sum = 1,a,b;clrscr();

for (a=1;a<=5;a++){

printf ("the multiplication table for %d\n",a);

for (b=1;b<=12;b++){

sum=a*b;printf("%d*%d=",a,b);printf("%d\n",sum);

}sum = 0;

}getch();}

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Exercise1) Write a program that will read in N numbers and print out their average. 2) Wap to print the following series for N given number 1+(1+2)+(1+2+3)+(1+2+3+4)………3) Wap to print the following series for N given number +

++++++++++++++++++++ ………..

4) Wap to print the following series for N given number 1 111 11111 1111111

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JUMPS IN LOOPS

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1. Loops perform a set of operations repeatedly until the control variable fails to satisfy the test – condition.

2. The number of times a loop is repeated is decided in advance and the test condition is written to achieve this.

3. Sometimes, when executing a loop it becomes desirable to skip a part of the loop or to leave the loop as soon as a certain condition occurs.

4. Jumps out of a Loop is Classified into three types

1. break;

2. continue;

3. goto;

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The break Statement1. A break statement is used to terminate of to exit a for, switch, while or do – while

statements and the execution continues following the break statement.

2. The general form of the break statement is

3. The break statement does not have any embedded expression or arguments.

4. The break statement is usually used at the end of each case and before the start of the next case statement.

5. The break statement causes the control to transfer out of the entire switch statement.

break;

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#include <stdio.h>

void main()

{

int i;

clrscr();

i = 1;

while (i < = 10)

{

printf (“The I Value is: %d \n”, i);

if (i = = 6)

{

printf (“The I value is Reached 6, So break of the programs\n”);

break;

}

++ i

}

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#include<stdio.h>void main (){

int num1,num2,choice;printf (“Enter the Two Numbers:\n”);scanf(“%d%d”,&num1,&num2);printf(“1 -> Addition\n””);printf(“2->Subtraction\n”);printf(“3->Multiplication\n”);printf(“4->Division\n”);printf (“Enter your Choice:\n”);scanf (“%d”, &choice);

switch (choice){

case 1: printf (“Sum is %d \n”, num1+num2); break;case 2:

printf (“Diif. is %d \n”, num1-num2); break;case 3: printf (“Product is %d \n”, num1*num2); break;case 4:

printf (“Division is %d \n”, num1/num2); break;default: printf (“Invalid Choice…..\n”);

}

getch(); }

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The continue Statement• The continue statement is used to transfer the control to the beginning of the loop, there

by terminating the current iteration of the loop and starting again from the next iteration of the same loop.

• The continue statement can be used within a while or a do – while or a for loop.

• The general form or the syntax of the continue statement is

• The continue statement does not have any expressions or arguments.

• Unlike break, the loop does not terminate when a continue statement is encountered, but it terminates the current iteration of the loop by skipping the remaining part of the loop and resumes the control tot the start of the loop for the next iteration.

continue;

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#include <stdio.h>

void main()

{

int i;

clrscr();

i = 1;

while (i < = 10)

{

printf (“The I Value is: %d \n”, i);

if (i = = 6)

{

printf (“The I value is Reached 6, But Continue this Programs\n”);

continue;

}

++ i

}

04/20/23 139

Sl.No. break continue

1. Used to terminate the loops or to exit loop

from a switch.

Used to transfer the control to the start ofloop.

2. The break statement when executed causes

immediate termination of loop containingit.

Continue statement when executed causesImmediate termination of the current

iterationof the loop.

Differences Between Break and Continue Statement

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The goto Statement• The goto statement is used to transfer the control in a loop or a function from one point to

any other portion in that program.

• If misused the goto statement can make a program impossible to understand.

• The general form or the syntax of goto statement is

• The goto statement is classified into two types

a. Unconditional goto

b. Conditional goto

goto label;Statement (s);…………….

label:statement (s);

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Unconditional Goto

The Unconditional goto means the control transfer from one block to another block without checking the test condition.

Example:

#include <stdio.h>

void main()

{

clrscr();

Start:

printf(“Welcome\n”);

goto Start;

getch();

}

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Conditional Goto

The Conditional goto means the control transfer from one block to another block with checking the test condition.

#include <stdio.h>void main(){

int a, b;clrscr();printf (“Enter the Two Value:\n”);scanf (“%d”, &a, &b);

if (a > b)goto output_1;

elsegoto output_2;

output_1:printf (“A is Biggest Number”);goto Stop;

output_2:printf (“B is Biggest Number”);goto Stop;

Stop:

getch();

}

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UNIT IVARRAYS AND FUNCTIONS

Arrays

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Definition of ArrayAn array is a fixed – size sequenced collection of elements of the

same data type. It is simply a grouping of like – type data. In its simplest form, an array can be used to represent a list of numbers, or list of names.(OR)

Array is a Collection of Homogenous Data Items Example1. List of employees in an organization.2. List of products and their cost sold by a store.3. Test Scores of a class of students.

Types of Array1. One Dimensional Array

2. Two Dimensional Array

3. Multi Dimensional Array

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One Dimensional Array

X

Y

Z

One Dimensional Array is defined any one of axis (X or Y or Z) in the graph

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ArraysSo far, we've been declaring simple variables

int i; It is also possible to declare an array of Several elements. an array is a variable that can hold more than one value , The declaration

int a[10]; declares an array, named a, consisting of ten elements, each of type int. We can represent the array a above with a picture like this:

•Arrays are zero-based: the ten elements of a 10-element array arenumbered from 0 to 9.

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Arrays

• An array uses a single identifier, together with an integer index, to create one variable that can hold many values

• An array is created the same as a “normal” variable, but with the addition of square brackets indicating the size of the array

• Each value in the array is called an element

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One Dimensional Arrays

Syntax data_type array_name[size];

Description Data_type valid data type in C languageArray_name name given to the arraySize are the size of the dimensions

Example int a[3];float b[4];

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Initializing Arrays

• An array is initialized using a code block containing comma-delimited values which match in position the elements in the array

• If there are values in the initialization block, but not enough to fill the array, all the elements in the array without values are initialized to 0 in the case of float or int, and NULL in the case of char

• If there are values in the initialization block, an explicit size for the array does not need to be specified, only an empty Array Element Operator is needed. C will count the values and size the array for you.

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Initializing Arraysint x [ 5 ] = { 1,2,3,4,5 }; size 10 bytescreates array with elements 0-4 values 1-5int x [ 5 ] = { 4,3 }; size 10 bytescreates array with elements 0-4 values 4,3,0,0,0int x [ ] = { 1,2,3 }; size 6 bytescreates array with elements 0-2 values 1,2,3char c [ 4 ] = { ‘M’ , ‘o’ , ‘o’ }; size 4 bytescreates array with elements 0-3 values M o o

NULL

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Arrays Cont’•The first element of the array is x[0], the second element is x[1]..

e.g x[0] = 10; x[1] = 20; x[2] = 30 x[3] = 40 x[4] = 50 Total = 150;This loop sets all ten elements of the array a to 0. int a[i]; int i; for(i = 0; i < 10; i = i + 1) a[i] = 0; To copy the contents of one array to another, you must again do so one by one:

int b[10]; for(i = 0; i < 10; i = i + 1) b[i] = a[i];

Printing Array Valuesfor(i = 0; i < 10; i = i + 1) printf("%d\n", a[i]);

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Array Basics

• An array has a fixed number of elements based on its creation

• The elements are ALWAYS numbered from 0 to 1 less than the array’s size

• Referencing an element outside of the created bounds is possible but not recommended

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Visual Representation of an Array

?

?

23

?

int x[4];

x[2]=23;

342901

342905

342909

342913

0

1

2

3

X

AddressOffset

Identifier

Value

04/20/23 156

The Array Element Operator [ ]

• The Array Element Operator is used to reference a specific array element

• The expression inside the Array Element must resolve to type int. This value is known as an index

• The value of the index can be any number, but care should be taken that the index falls within the bounds of the array. The bounds of an array are defined as 0 to 1 less than the size of the array

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Array Example#include <stdio.h>

int main(void)

{

int x[5];

x[0]=23; valid

x[2.3]=5; invalid: index is not an int

x[6]=45; valid but not recommended

return 0;

}

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A Simple Array Example#include <stdio.h>int main(void)

{int i , x[ 5 ] , total = 0 ;for ( i = 0 ; i < 5 ; i++ )

{printf( “Enter mark %d” , i );scanf ( “%d” , &x[ i ] );}

for ( i = 0 ; i < 5 ; i++ )total = total + x[ i ];

printf ( “The average is %d” , total / 5 );return 0;}

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ARRAYS

• DON'T declare arrays with subscripts larger than you will need; it wastes memory.

• DON'T forget that in C, arrays are referenced starting with subscript 0, not 1.

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Sample program#include<stdio.h>main(){ int a[5],i; printf(‘enter the array elements”); for(i = 0;i<5;i++) scanf(“%d”,&a[i]); printf(“Array in the reverse order”); for(i = 5;i>0;i--) printf(“%d”,a[i];}

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#inlcude<stdio.h>#define Max 5;main();{ int a[Max], i, min; int pos = 0; printf(“Enter the array elements”); for(i=0;i<5;i++) scanf(‘%d”,&a[i]); min = a[0]; for(i=1;i<Max;i++) if(a[i] < min) { min = a[i]; pos = i; } printf(“ Minimum Value = %d” , min); printf(“ Position of the Minimum Value = %d” , pos);}

04/20/23 162

Exercise Identify the errors if any,

1) #define Max 1.5; main() { int a[Max]; }

2) main() { int i,a[5]; for(i=0;i<5;i++); a[i] = 0; }

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main(){ int size; scanf(“%d”,&size); int arr[size]; for(int i=1;i<size;i++) { scanf(“%d”,&arr[i]); printf(“%d”,arr[i]); }}

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• State whether the following are true or false

1) The array int num[26] has twenty-six elements.2) The expression num[1] designates the first element in the

array.3) The expression num[27] designates the twenty-eighth

element in the array.

• What is the difference between the 5’s in these two expressions

int num[5]; num[5] = 200;

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Two-Dimensional Arrays

• Two-dimensional Array: a collection of a fixed number of components arranged in two dimensions– All components are of the same type

• The syntax for declaring a two-dimensional array is:dataType arrayName[intexp1][intexp2];

where intexp1 and intexp2 are expressions yielding positive integer values

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Two-Dimensional Arrays (continued)

• The two expressions intexp1 and intexp2 specify the number of rows and the number of columns, respectively, in the array

• Two-dimensional arrays are sometimes called matrices or tables

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Two Dimensional Array

X

Y

Z

Two Dimensional Array is defined any Two of axis of XY or YZ or ZX in the graph

04/20/23 168

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Two Dimensional Arrays

Syntax data_type array_name[size_1][size_2];

Description Data_type valid data type in C languageArray_name name given to the arraySize_1 is the row size of the arraySize_2 is the column size of the array

Example int a[3][3];float b[4][4];Int a[3][2];

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Two Dimensional Array Initializing int table [2][3] = {0,0,0,1,1,1};

int table [2][3] = {{0,0,0},{1,1,1}};

int table [2][3] = {

{0,0,0},

{1,1,1}

};

int table [ ][3] = {

{0,0,0}

{1,1,1}

};

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Two Dimensional Array Initializing If the values are missing in an initializer, they are automatically set to zero. For instance, the statement

int table [2][3] = {

{1,1},

{2}

};

will initialize the first two elements of the first row to one, the first element of the second row to two , and all other elements to zero.

When all the elements are to be initialized to zero, the following short – cut method may be used.

int m[3][5] = { {0},{0},{0} };

The first element of each row is explicitly initialized to zero while other elements are automatically initialized to zero, The following statement will also achieve the same result:

int m[3][5] = {0,0};

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Accessing Array Components

• The syntax to access a component of a two-dimensional array is:arrayName[indexexp1][indexexp2]

where indexexp1 and indexexp2 are expressions yielding nonnegative integer values

• indexexp1 specifies the row position and indexexp2 specifies the column position

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0 1 2

0

1

2

3

4 25.75

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Multi – Dimensional Arrays• Three or More Dimensional Array is called the

Multi – Dimensional Arrays.

X

Y

ZThree Dimensional array defined in any three of axis of XYZ OR YZX OR ZXY in the graph

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Multi Dimensional Arrays• This arrays have more than one dimensions.

Syntax data_type array_name[size1][size2]…….[sizen];

Description Data_type valid data type in C languageArray_name name given to the arraySize1,size2 are the sizes of the dimensions

Example Int a[3][3][3];Float b[4][4][4];

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CHARACTER ARRAYS AND STRINGS

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Character and Strings• An char array is a group of characters that store related data• A String is a special char array that does not store related data, but

a single piece of data made up of a number of characters OR A string is a sequence of character that is treated as a single data item. Any group of characters defined between double quotation marks is a string constant.

• Example: Grades can be stored in a char array with the values A,B,C,D,F; when we want to print a specific grade we use only 1 element of the array

• Example: But for grades like “Pass” and “Fail” we must print ALL the elements

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String Conti…

• Most Computers languages have a string data type; C does NOT

• There are 3 ways to store strings in memory– Fixed Length– Stored Length– Terminated

• C adopts the Terminated String approach• A string in C is an array of chars terminated by

the String Terminator or NULL character \0

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Common String Operation

1. Reading and Writing Strings2. Combining strings together3. Copying one string to another4. Comparing strings for equality5. Extracting a portion of a string

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Declaring and Initializing of StringThe General form of String is

char string_name [size];

Example:

char city [10];

char name[30];

When the complier assigns a character string to a character array, it automatically supplies a multicharacter (‘\0’) at the end of the string. Therefore, the size should be equal to the maximum number of characters in the string plus one.

C Permits a character array to be initialized in either of the following two forms:

char city [9] = “ NEW YORK”;

char city [9] = {‘N’.’E’,’W’,’ ‘,’Y’,’O’,’R’,’K’,’\0’);

C also permits us to initialize a character array without specifying the number of elements. In such cases, the size of the array will be determined automatically, base on the number of elements initialiazed. For Example, the statement

char string [ ] = {‘G’,’O’,’O’,’D’,’\0’};

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DeclaringConti….We can also declare the size much larger than the string size in the initializer. That is, the statement.

char str[9] = “GOOD”;

G O O D \0 \0 \0 \0 \0

The following declaration is illegal.(I) char str[5];

str = “GOOD”;This will result in a compile time error. Also note that we cannot separate the

initialization from declaration.(II) char s1[4] = “abc”;

char s2[4];s2 = s2; /* Error */

is not allowed. An array name cannot be used as the left operand of an assignment operator.

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Creating a String in C

h

i

!

hi

!

/0

array string1820

1821

1822

2820

2821

2822

2823

04/20/23 183

READING STRINGS FROM TERMINALThe familiar input function scanf can be used with %s format specification to read in a string of characters.

Example:

char address [10];

scanf(“%s”,address);

The problem with the scanf function is that it terminates its input on the first white space it finds. Therefore, if the following line of text is typed in at the terminal,

NEW YORK

then only the string “NEW” will be read into the array address, since the blank space after the word ‘NEW’ will terminate the string reading.

The scanf calls in the case of character arrays, the ampersand (&) is not required before the variable name.

The address array is created in the memory as shown below:

N E W \O ? ? ? ? ? ?

Note that the unused locations are filled with garbage.

If we want to read the entire line “NEW YORK”, then we may use two character arrays of approximate sizes. That is,

char adr1[5], adr2[5];

scanf(“%s %s”,adr1,adr2);

With the line of text

NEW YORK

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READING STRINGS FROM TERMINALWe can also specify the field width using the form %ws in the scanf statement for reading a specified number of characters from the input string.

Example: scanf(“%ws”,name);

Here two things may happen.

1. The width w is equal to or greater than the number of characters typed in. The entire string will be

stored in the string variable.

2. The width w is less than the number of characters in the string. The excess characters will be

truncated and left unread.

Consider the following statements:

char name [10];

scanf(“%5s”,name);

The input string RAM and KRISHNA will be stored as:

R A M \0 ? ? ? ? ? ?

K R I S H \0 ? ? ? ?

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Reading a Line of Text

We have seen just now that scanf with %s or %ws can read only strings without white spaces. That is, they cannot be used for reading a text containing more than one word. However, C Supports a format specification known as the edit set conversion code % [..] that can be used to read a line containing a variety of characters, including white spaces. Recall that we have used this conversion code in the program segment

char line [80];

scanf (“%[^\n]”,line);

printf(“%s”,line);

will read a line of input from the keyboard and display the same on the screen. We would very rarely use this method.

Using getchar and gets Functions

To read a single character from the terminal, using the function getchar. We can use this function repeatedly to read successive single characters from the input and place them into a character array. Thus, an entire line of text can be read and stored in an array. The reading is terminated when the newline character (‘\n’) is entered and the null character is then inserted at the end of the string. The getchar function call takes the form:

char ch;

ch = getchar ( );

Note that the getchar function has no parameters.

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#include <stdio.h>

void main(){

char line[81], character;int c;

c = 0;

printf("Enter text. Press <Return> at end\n");

do{

character = getchar( );line[c] = character;c++;

}while(character != '\n');

c = c - 1;line [c] = '\0';printf("\n%s\n", line);

}

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getchar and gets Conti….

Another and more convenient method of reading a string of text containing white spaces is to use the library function gets available in the <stdio.h> header file. This is a simple function with one string parameter and called as under.

gets (str);

str is string variable declared properly. It reads characters into str from the keyboard until a new line character is encountered and then appends a null character to the string. Unlike scanf, it does not skip white spaces. For example the code segment

char line [80];

gets (line);

printf(“%s”,, line);

reads a line of text from the keyboard and displays it on the screen. The last two statements may be combined as follows:

printf(“%s”,gets(line));

C does not provide operators that work on strings directly. For instance we cannot assign one string to another directly. For example, the assignment statements.

string = “ABC”

string1 = string2;

are not valid.

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#include<stdio.h>

void main(){

char string1[80],string2[80];int i;

printf("Enter a string \n");printf("?");

scanf("%s",string2);for(i=0;string2[i] != '\o'; i++)

string1[i] = string2[i];

string1[i] = '\o';

printf("\n");printf("%s\n", string1);printf("Number of characters = %d\n",i);

}

04/20/23 189

WRITING A STRINGS TO SCREEN

We have used extensively the printf function with %s format to print strings to the screen. The format %s can be used to display an array of characters that is terminated by the null character. For example, the statement

printf(“%s”, name);

can be used to display the entire contents of the array name.

We can also specify the precision with which the array is displayed. For instance, the specification

%10.4

Indicates that the first four characters are to be printed in a field width of 10 columns.

However, if we include the minus sign in the specification (e.g., %-10.4s), the string will be printed left-justified.Using putchar and puts Functions

Like getchar, C supports another character handling function putchar to output the values of character variables. It takes the following form:

char ch = ‘A’;

putchar (ch);

The function putchar requires one parameter. This statement is equivalent to:

printf(“%c”,ch);

We have used putchar function to write characters to the screen. We can use this function repeatedly to output a string of characters stored in an array using a loop:

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Example:char name[6] = “PARIS”;for(i=0;i<5;i++)

putchar (name[i]);putchar(‘\n’);

Another and more convenient way of printing string values is to use the function puts declared in the header file <stdio.h>. This is a one parameter function and invoked as under:

puts (str);Where str is a string variable containing a string value. This prints the value of the string variable str and then moves the cursor to the beginning of the next line on the screen. For example, the program segment

char line [80];gets (line);puts (line);

Reads a line of text from the keyboard and displays it on the screen. Note that the syntax is very simple compared to using the scanf and printf statements

Using putchar and puts Functions Conti…

04/20/23 191

The C Library supports a large number of string – handling function that can be used to carry out many of the string manipulations.

The most commonly used string – handling functions.

STRING HANDLING FUNCTIONS

Function Actionstrcat ( ) Concatenates two strings

strcmp ( ) Compares two strings

strcpy ( ) Copies one strings over another

strlen ( ) Finds the length of a string

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Function

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C function can be classified into two categories, namely, library functions and user – defined functions. main is an example of user – defined functions. printf and scanf belong to the category of library functions. We have also used other library functions such as sqrt, cos, strcat, etc.

The main distinction between these two categories is that library functions are not required to be written by us whereas a user – defined function has to be developed by the user at the time of writing a

program.

Introduction

Some Characteristic of modular programming are:

1. Each module should do only one thing.

2. Communication between modules is allowed only by a calling module.

3. A module can be called by one and only one higher module

4. No communication can take place directly between modules that do not have calling – called relationship

5. All modules are designed as single – entry, single – exit systems using control structures

04/20/23 194

1. Every program must have a main function to indicate where the program has to begin its execution. While it

is possible to code any program utilizing only main function. It leads to a number of problems.

2. The program may become too large and complex and as a result the task of debugging, testing, and

maintaining becomes difficult.

3. If a program is divided into functional parts, then each part may be independently coded and later

combined into a single unit. These subprograms called ‘functions’ are much easier to understand, debug,

and test.

4. The length of a source program can be reduced by using functions at appropriate places. This factor is

particularly critical with microcomputers where memory space is limited.

5. It is easy to locate and isolate a faulty function for further investigations.

6. A function may be used by many other programs.

Need for User – Defined Functions

04/20/23 195

DEFINITION• A function is a named, independent section of C code that performs a

specific task and optionally returns a value to the calling program.

• A function is named

• A function is independent.

• A function performs a specific task.

• A function can return a value to the calling program.

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Function COND…

• FUNCTION DECLARATION

• FUNCTION DEFINITION

• FUNCTION INVOCATION (FUNCTION CALL)

04/20/23 197

FUNCTION DEFINITION SYNTAXA function definition, also known as function implementation shall include the following elements.

1. Function Name

2. Function Type

3. List of Parameters

4. Local variable declarations

5. Function Statements

6. A Return statement

All the six elements are grouped into two parts, namely,

1. Function header (First three Elements)

2. Function Body (Second three Elements)

function_type function_name(parameter_list)

{

local variable declaration;

executable statement_1;

executable statement_2;

---------------------------------

---------------------------------

return statement;

} Example:

float mul ( float x, float y)

{

float result;

result = x * y;

return (result);}

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FUNCTION PROTYPING OR FUNCTION DECLARATION

• A function prototype is a very important feature of modern C programming

• It must be added to a C program just before the main function, if we call that function before defining it

• It tells the compiler what type of value the function returns, numbers and types of parameters, and order in which these parameters are expected.

• There is no need for a prototype if the function is called after its definition

04/20/23 199

FUNCTION DECLARATION SYNTAX

Like variables, all functions in a C program must be declared, before they are invoked, A function declaration (also known as function prototype) consists of four parts.

1. Function type (return type)

2. Function name

3. Parameter list

4. Terminating semicolon

The general format is

Function_type function_name(parameter_list);

Example:

float mul (float x, float y);

04/20/23 200

Function Definition

A simple format of a C function definition is as

follows:

return-value-type function-name(parameters)

{

Declarations;

Statements;

Return (expression);

}

Function Prototype

04/20/23 201

Sl.No. Function prototype Function definition

1. It declares the function. It defines the function

2. It ends with a semicolon. It doesn’t end with a semicolon.

3. Declaration need not include parameters.

Definition should include names for theparameters.

Difference Between Function Prototyping and Function Definition

04/20/23 202

WORKING PRINCIPLES

04/20/23 203

Function Terminologies

Local and global variables– Local: a variable defined inside a function– Global: a variable defined outside of functions

Sl.No. Local Variables Global Variables

1. These are declared within the body of the function.

These are declared outside the function.

2. These variables can be referred only within the function in which it is declared. The values of the variables disappear once the function finishes its execution.

These variable can be referred from any part of the program value of variables disappear only after the entire execution or the program.

04/20/23 204

Formal and Actual Parameters

• In C, there are two types of parameters

• Formal parameters appear in the prototype and definition, and are representative of the data types the function expects to receive

• Actual parameters appear only in a function call and are the actual data passed

04/20/23 205

Example #include <stdio.h>void MyFun( int ); Formal Parameterint main( void )

{ int x=3;

printf( “x has a value of %d”, x); MyFun( x ); Actual Parameter

printf( “x has a value of %d”, x); return 0; Parameter Passing}

void MyFun( int x ) Formal Parameter{ printf( “x has a value of %d”, x); x = 77; printf( “x has a value of %d”, x);}

04/20/23 206

Function prototype anddefinition

#include <stdio.h>int mod(int , int); /* Function Prototype */void main() { printf("The mod is: %d ", mod(4,5)); }/* Function Definition */int mod(int x, int y) { return x % y; }

04/20/23 207

CATEGORIES OF FUNCTIONS

Category 1: Functions with no arguments and no return values.

Category 2: Functions with arguments and no return values.

Category 3: Functions with arguments and one return value.

Category 4: Functions with no arguments but return a value.

Category 5: Functions that return multiple values.

04/20/23 208

Function with No return typeand No arguments

void main()

{

…….

…….

…….

func1();

…….

}

void func1()

{

…….

…….

…….

…….

}

04/20/23 209

#include<stdio.h>void add();void main() { add(); }void add() { int a,b,c; printf(“enter any two numbers”) scanf(“%d%d”,&a,&b); c= a+b; printf(“the addition of %d and %d is %d”,a,b,c);

}

04/20/23 210

Function with No return typeand with arguments

Void main()

{

…….

…….

…….

func1(x,y);

…….

}

func1(a,b)

{

…….

…….

…….

…….

}

04/20/23 211

#include<stdio.h>void add(int,int);void main() { int x,y,c; printf(“enter any two numbers”) scanf(“%d%d”,&x,&y); add(x,y); }void add(int a,int b) { int c; c= a+b; printf(“the addition of %d and %d is %d”,a,b,c); }

04/20/23 212

Function with return typeand with arguments

void main()

{

…….

…….

…….

int func1(x,y);

…….

}

int func1(a,b)

{

…….

…….

…….

…….

}

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#include<stdio.h>int add(int,int);Void main() { int x,y,c; printf(“enter any two numbers”) scanf(“%d%d”,&x,&y); c = add(x,y); printf(“The Result = %d ”,c);

}int add(int a ,int b) { int c; c= a+b; return (c);

}

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Function with return typeand No arguments

void main()

{

…….

…….

…….

int func1();

…….

}

int func1()

{

…….

…….

…….

…….

}

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#include<stdio.h>int add();Void main() { int c; c = add(); printf(“The Result = %d ”,c);

}int add() { int a,b,c; printf(“enter any two numbers”)

scanf(“%d%d”,&a,&b); c= a+b; return (c);

}

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Functions that return multiple values#include <stdio.h>void interchange (int *a , int *b)void main() { int i=5,j=10; printf(“Before : I and J value is %d and %d”,I,j);

interchange(&i,&j);printf(“After : I and J value is %d and %d”,I,j);

}void interchange (int *a, int *b) { int t;

t=*a*a=*b*b=t

}

O/p: Before : I and J value is 5 and 10 After : I and J value is 10 and 5

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Function without a prototype

#include <stdio.h>int sum(int x, int y) { return x+y; }void main() { printf("The sum is: %d ", sum(4,5)); }

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Parameter Passing Methods

• In C there are two ways of passing parameters to a function

Call by ValueCall by Reference

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Call by value

Copy of data passed to functionChanges to copy do not change originalPrevent unwanted side effects

This Method copies the value of actual parameters(calling program) into the formal parameters(called program) of the functions.

Here the changes of the formal parameters cannot affect the actual parameters. Because only the copy of actual arguments were passed.

A function can return only one value per call.

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Example#include <stdio.h>int cube (int)void main() { int n=5; printf(“Cube of %d is %d”,n,cube(n));

}

int cube (int x); { x=x*x*x; return x; }

O/p: Cube of 5 is 125

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Call by reference Function can directly access dataChanges affect original

It is another way of passing parameter to the functions here the address of arguments are copied into the parameters inside the functions.

The address is used to access the actual arguments used in the call.

By using this we can make a function to return more the one value(indirectly).

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Example#include <stdio.h>void interchange (int *a , int *b)void main() { int i=5,j=10; printf(“Before : I and J value is %d and %d”,I,j);

interchange(&i,&j);printf(“After : I and J value is %d and %d”,I,j);

}void interchange (int *a, int *b) { int t;

t=*a*a=*b*b=t

}O/p: Before : I and J value is 5 and 10 After : I and J value is 10 and 5

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Call by valueVs

Call by reference • Call by value

Copy of data passed to functionChanges to copy do not change originalPrevent unwanted side effects

• Call by reference Function can directly access dataChanges affect original

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#include <stdio.h>void swap(int, int);void main()

{int num1, num2;num1 = 10; num2 = 20;swap ( num1, num2 );printf("%d %d\n", num1, num2);

}void swap(int val1, int val2)

{int temp;temp = val1;val1 = val2;val1 = temp;

}

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Swap two integers using call by value(cont.)

• In the above example, we passed parameters by value, a copy is made of the variable and thus any change made to the parameters val1 and val2 will not be passed back to the main function

• The main function will not know anything aboutthe swapping of val1 and val2 Therefore, the output of the above program will be….?

• Normally if we wished to pass back a value wewould use return or we would pass the parametersby reference

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Nested Functions

In C , it provides a facility to write one function with in another function. This is called nesting of functions

Main(){---------func1();------------------}

func1(){---------func2();------------------}

func2(){------------------------------------}

Recursion

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Recursion

Recursion is a process of calling the same function itself again and again until same condition is satisfied.

This is used for repetitive computation in which each action is satisfied in terms of a previous result•A function can call itself

–Directly–Indirectly

Function1(){

-----Function1();

-----}

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Recursion vs. Iteration• Repetition

– Iteration: explicit loop– Recursion: repeated function calls

• Termination– Iteration: loop condition fails– Recursion: base case recognized

• Both can have infinite loops• Balance between performance (iteration) and

good software engineering (recursion)

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Sl.No. Iteration Recursion

1. Iteration explicitly user a repetitionstructure.

Recursion achieves repetition throughtrepeated function calls.

2. Iteration terminates when the loopcontinuation condition fails.

Recursion terminates when a base case is

reached.

3. Iteration keeps modifying the counteruntil the loop continuation condition

fails.

Recursion keeps producing simple versions

of the original problem until the base case is

reached.

4. An infinite loop occurs when the loop step

continuation test never becomes false.

An infinite loop occurs if the recursion doses

not reduce the problem each time in amanner that converges the base case.

5. Iteration normally occurs within a loop so

extra memory assignment is omitted.

Recursion causes another copy of thefunction & hence a considerable memoryspace is occupied.

6. It reduces the processor operating time.

It increases the processor operating time.

Difference Between Iteration and Recursion

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Example: fibonacci.c

function Fibonacci ( n ){ if ( n is less than or equal to 1 ) then return n else return Fibonacci ( n - 2 ) + Fibonacci ( n - 1 )}

/* Compute the n-th Fibonacci number, when=0,1,2,... */

long fib ( int n ){ if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 );}

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Example: Computation of fib(4)

+fib(2) fib(3)

fib(4)


4

4

4 4

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fib(2) fib(3)+

fib(4)


2

2

2 2

+fib(0) fib(1)

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fib(2) fib(3)+

fib(4)


0

0

+fib(0) fib(1)

0

04/20/23 235


fib(2) fib(3)+

fib(4)


0

0

+0 fib(1)

0

04/20/23 236


fib(2) fib(3)+

fib(4)

+ fib(1)0


2

2

220

04/20/23 237


fib(2) fib(3)+

fib(4)


1

1

+ fib(1)0

1

04/20/23 238


fib(2) fib(3)+

fib(4)


1

1

+ 10

1

04/20/23 239


fib(2) fib(3)+

fib(4)

+0 1


2

2

0 21

04/20/23 240


1 fib(3)+

fib(4)


2

2

0

+0 1

21

04/20/23 241


+ fib(3)

fib(4)


4

4

4 4

1

+0 1

1

04/20/23 242


+ fib(3)

fib(4)


3

3

3 3

1

+0 1 +fib(1) fib(2)

04/20/23 243


+ fib(3)

fib(4)

1

+0 1 +fib(1) fib(2)


1

11

04/20/23 244


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)


1

11

04/20/23 245


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)


3

3

3 31

04/20/23 246


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)


2

2

2 2

+fib(0) fib(1)

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+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+fib(0) fib(1)


0

00

04/20/23 248


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+0 fib(1)


0

00

04/20/23 249


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+0 fib(1)


2

2

2 20

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+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+0 fib(1)


1

11

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+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+0 1


1

11

04/20/23 252


+ fib(3)

fib(4)

1

+0 1 +1 fib(2)

+0 1


2

2

2 20 1

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+ fib(3)

fib(4)

1

+0 1 +1 1

+0 1


2

2

2 20 1

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+ fib(3)

fib(4)

1

+0 1 +1 1

+0 1


3

3

3 31 1

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+ 2

fib(4)

1

+0 1 +1 1


3

3

3 31 1

+0 1

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+ 2

fib(4)

1

+0 1 +1 1

+0 1


4

4

4 41 2

04/20/23 257


+ 2

3

1

+0 1 +1 1

+0 1


4

4

4 41 2

04/20/23 258


+ 2

3

1

+0 1 +1 1

+0 1

Thus, fib(4) returns the value 3

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int main(void){ int number;

printf("Enter number: "); scanf("%d", &number);

printf("Fibonacci(%d) = %ld\n", number, fib(number));

return 0;}

Example: fibonacci.c

Sample main() for testing the fib() function:

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Scope

Where can you use a variable which is declared in a function?

• In that function only• Not in a calling function• Not in a called function

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Scope: Local Variables

• Formal parameters: only accessible whilst a function is executing

• Variables declared in a function body: only accessible whilst the function is executing

• In fact, this is true of every block in a program

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Exercise

• Write a program to find the factorial using a functions.

• Write a program to find the value of xn. For any

given values of x and n .

Passing arrays to Functions

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Arrays to the function in One dimensional • An entire array can be transferred to a function as a parameter.• Actual parameter : the array name is enough without subscripts to transfer an

array.• Formal parameter : must be declared as an array to receive the values from main

program.

syntax :

void func(int,int[])main() void func(int x, int arr[10]){ { int a[10],i; ………… func(i,a); …………} }

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Three Rules of Pass an Array to a Function

1. The function must be called by passing only the name of the array.

2. In the function definition, the formal parameter must be an array type; the

size of the array does not need to be specified.

3. The function prototype must show that the argument is an array.

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Sample program#include<stdio.h>#inlcude<conio.h>void add(int[])void main(){ int i,arr[10]; printf(“Enter 10 elements of the

array”); for(i = 0;i<10;i++) scanf(‘%d”,&arr[i]); add(arr);}

void add(int a[]){ int i,sum = 0; for(i = 0;i<10;i++) sum = sum+a[i];printf(“ the value of sum is %d”,

sum);}

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Changing an Array in a Function#include <stdio.h>

void fun ( int [ ] )

int main(void)

{

int array[ ] = { 1 , 2 , 3 , 4 , 5 };

fun ( array );

printf ( “%d” , array [ 3 ] ); Will print 20

return 0;

}

void fun ( int x[ ] )

{

x[3] = 20;

return;

}

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#include<stdio.h>

void main(){

float largest(float a[ ], int n);float value [4] = {2.5,-4.75,1.2,3.67};

printf("%f\n",largest(value,4);}

float largest(float a[ ], int n){

int i;float max;

max = a[0];

for(i=1; i<n; i++)if(max < a[i])

max = a[i];return(max);

}

Largest of Given Numbers

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Sorting of Given Numbers#include<stdio.h>

void main(){

int i;int mark[5] = {40,90,73,81,35};

printf("Marks before sorting\n");for(i = 0;i<5;i++)

printf("%d",marks[i]);

printf("\n\n");

sort(5,marks);

printf("Marks after sorting\n");for(i = 0;i<5;i++)

printf("%4d",mark[i]);printf("\n");

}

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Sorting of Given Numbers Conti….

void sort(int m,int x[]){

int i,j,t;

for(i=0;i<m-1;i++)for(j=i+1;j<m;j++)

if (x[i] > x[j]){

t = x[i];x[i] = x[j];x[j] = t;

}}

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Arrays to the function in Two dimensional

Like simple arrays, we can also pass multidimensional array to functions. The approach is similar to the one we did with one – dimensional arrays.

The rules are simple.

1. The function must be called by passing only the array name.

2. In the function definition, we must indicate that the array has two

dimensions by including two sets of brackets.

3. The size of the second dimension must be specified.

4. The prototype declaration should be similar to the function header.

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Calculates the average of the values in a two – dimensional matrix#include<stdio.h>

void main(){

int M = 3, N = 2;double average (int [] [N],int,int);double mean;int matrix [M][N] = {{1,2},{3,4},{5,6}};mean = average(matrix, M, N);printf("The Mean of the Two Dimensional Array is: %f",mean);

}

double average(int x [ ] [N],int M,int N){

int i,j;

double sum = 0.0;for(i=0;i<m;i++)

for(j=1;j<N;j++)sum = sum + x[i][j];

return (sum / (M * N);}

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Passing Strings to FunctionsThe Strings are treated as character arrays in C, the rules for passing strings to functions are very similar to those for passing arrays to functions.

Basic Rules are:

1. The string to be passed must be declared as a formal argument of the function when it is

defined.

Example:

void display(char item_name[])

{

----------------

----------------

}

2. The function prototype must show that the argument is a string. For the above function

definition, the prototype can be written as

void display(char str[ ])

3. A call to the function must have a string array name without subscripts as its actual arguments.

Example:

display(names);

where names is a properly declared string array in the calling function.

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POINTER CONCEPT

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Pointer DeclarationConsider the declarclaation,

int i=3;

This declaration tells the C Compiler to,

(a) Reserve space in memory to hold the integer value.

(b) Associate the names i with this memory location.

(c) Store the value3 at this location.

i

65524

We can see that the computer has selected memory location 65524 as the place to store the value 3. It is not fixed because the computer can change the location later. We can print this address number through the following program:

main( )

{

int i=3;

printf(“\n Address of i= %u”, &i);

printf(“\n Value of i= %d:, i);

}

Output: Address of i= 65524

Value of i= 3.

3

Location Name

Value at Location

Location Number

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• Look at the first printf( ) statement carefully. ‘&’ used in this statement is C’s ‘address of’ operator.

• The expression &i returns the address of the variable i, which in this case happens to be 65524.

• Hence it is printed out using %u, which is a format specifier for printing an unsigned integer.

• We have been using the ‘&’ operator all the time in the scanf( ) statement.

• The other pointer operator available in C is ‘*’, called ‘value at address’ operator.

• It gives the value stored at a particular address. The ‘value at address’ operator is also called ‘indirection’ operator.

• Observe carefully the output of the following program:

main( )

{

int i = 3 ;

printf ( "\nAddress of i = %u", &i ) ;

printf ( "\nValue of i = %d", i ) ;

printf ( "\nValue of i = %d", *( &i ) ) ;

}

The output of the above program would be:

Address of i = 65524

Value of i = 3

Value of i = 3

• Note that printing the value of *( &i ) is same as printing the value of i.

• The expression &i gives the address of the variable i. This address can be collected in a variable, by saying,

j = &i ;

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•But remember that j is not an ordinary variable like any other integer variable. It is a variable that contains the address of other variable (i in this case).

•Since j is a variable the compiler must provide it space in the memory. Once again, the following memory map would illustrate the contents of i and j.

i j

65524 65522

•As you can see, i’s value is 3 and j’s value is i’s address.

•But wait, we can’t use j in a program without declaring it. And since j is a variable that contains the address of i, it is declared as,

int *j ;

•This declaration tells the compiler that j will be used to store the address of an integer value.

•In other words j points to an integer. How do we justify the usage of * in the declaration,

int *j ;

•Let us go by the meaning of *. It stands for ‘value at address’. Thus, int *j would mean, the value at the address contained in j is an int.

3 65524

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• Here is a program that demonstrates the relationships we have been discussing.

main( )

{

int i = 3 ;

int *j ;

j = &i ;


printf ( "\nAddress of i = %u", j ) ;

printf ( "\nAddress of j = %u", &j ) ;

printf ( "\nValue of j = %u", j ) ;


printf ( "\nValue of i = %d", *( &i ) ) ;

printf ( "\nValue of i = %d", *j ) ;

}




Address of j = 65522

Value of j = 65524

Value of i = 3

Value of i = 3

Value of i = 3

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• Look at the following declarations,

int *alpha ;

char *ch ;

float *s ;

• The declaration float *s does not mean that s is going to contain a floating-point value. What it means is, s is going to contain the address of a floating-point value.

• Similarly, char *ch means that ch is going to contain the address of a char value. Or in other words, the value at address stored in ch is going to be a char.

Double Pointer:

The concept of pointers can be further extended. Pointer, we know is a variable that contains address of another variable. Now this variable itself might be another pointer. Thus, we now have a pointer that contains another pointer’s address.

The following example should make this point clear.

main( )

{

int i = 3, *j, **k ;

j = &i ;

k = &j ;


printf ( "\nAddress of i = %u", j ) ;

printf ( "\nAddress of i = %u", *k ) ;

printf ( "\nAddress of j = %u", &j ) ;

printf ( "\nAddress of j = %u", k ) ;

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printf ( "\nAddress of k = %u", &k ) ;

printf ( "\nValue of j = %u", j ) ;

printf ( "\nValue of k = %u", k ) ;


printf ( "\nValue of i = %d", * ( &i ) ) ;

printf ( "\nValue of i = %d", *j ) ;

printf ( "\nValue of i = %d", **k ) ;

}







Address of k = 65520

Value of j = 65524

Value of k = 65522

Value of i = 3

Value of i = 3

Value of i = 3

Value of i = 3

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• Remember that when you run this program the addresses that get printed might turn out to be something different, However, with these addresses too the relationship between i, j and k can be easily established.

i j k

65524 65522 65520

• Observe how the variables j and k have been declared,

int i, *j, **k ;

• Here, i is an ordinary int, j is a pointer to an int (often called an integer pointer), whereas k is a pointer to an integer pointer.

• We can extend the above program still further by creating a pointer to a pointer to an integer pointer.

Back to Function Calls

The two types of function calls—call by value and call by reference. Arguments can generally be passed to functions in one of the two ways:

(a) sending the values of the arguments

(b) sending the addresses of the arguments

• In the first method the ‘value’ of each of the actual arguments in the calling function is copied into corresponding formal arguments of the called function.

• With this method the changes made to the formal arguments in the called function have no effect on the values of actual arguments in the calling function.

3 65524 65522

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• The following program illustrates the ‘Call by Value’.

main( )

{

int a = 10, b = 20 ;

swapv ( a, b ) ;

printf ( "\na = %d b = %d", a, b ) ;

}

swapv ( int x, int y )

{

int t ;

t = x ;

x = y ;

y = t ;

printf ( "\nx = %d y = %d", x, y ) ;

}


x = 20 y = 10

a = 10 b = 20

• Note that values of a and b remain unchanged even after exchanging the values of x and y.

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• In the second method (call by reference) the addresses of actual arguments in the calling function are copied into formal arguments of the called function.

• This means that using these addresses we would have an access to the actual arguments and hence we would be able to manipulate them.

• The following program illustrates this fact.

main( )

{

int a = 10, b = 20 ;

swapr ( &a, &b ) ;

printf ( "\na = %d b = %d", a, b ) ;

}

swapr( int *x, int *y )

{

int t ;

t = *x ;

*x = *y ;

*y = t ;

}

• The output of the above program would be:

a = 20 b = 10

• Note that this program manages to exchange the values of a and b using their addresses stored in x and y.

Storage class

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Storage class

• Every variable or constant possesses a data type• In addition to the data type, a variable possesses an attribute called

storage class.

where v1,v2 are the variables data_type is the valid data type in c language storage_class gives information regarding lifetime and scope.

Storage_class data_type v1,v2,v3,………………..vn.

04/20/23 286

Storage class cont’

• Lifetime Lifetime or Longetivity of a variable refers to the duration for which the

variable retains a given value during the execution of a program.

• Scope

It is the portion of the program in which the variable may be visible or available .It can classified into two types

Type 1: Local variable (or) private variable (or) internal variable. Type 2: Global variable (or) public variable (or) external variable.

04/20/23 287

Types

Sl.No Types of Storage Class Reserved words

1 Automatic auto

2 Register register

3 Static static

4 External extern

04/20/23 288

Automatic variables

• By default all variables are automatic storage class.• Their memory space is automatically allocated as the

variable is declared.• These variables are given only temporary memory space

and after the execution all the automatic variables will get disposed.

• It can not be accessed directly by other functions.

04/20/23 289

Sample Program#include<stdio.h>Void main(){ float f1 = 10.2; { float f1 = 40.00; { float f1 = 33.9; printf(“the value of f1 in block 3 is %f”,f1); } printf(“the value of f1 in block 2 is %f”,f1); }printf(“the value of f1 in block 1 is %f”,f1);}

04/20/23 290

Static Variables• The variables are declared with static keyword.• It can be internal static (or) external static based on the place of its

declaration.• Both are declared using the keyword static.• The storage used by an static variable in a block is not lost after the

completion of the execution.• Even after the termination of the block, the value of the static variable

is available.• If the value is changed during the execution the recent value is

retained. • When the execution enters the next time the same block, the

initialiser is neglected and the recently stored value is retained.

04/20/23 291

Sample Program

#include<iostream.h>

#include<conio.h>

int fun(int);

void main()

{

int i,x;

clrscr();

for(i=1;i<=10;i++)

{

x = fun(i);

cout<<"The I Value is:"<<x<<endl;

}

getch();

}

int fun(int a)

{

auto int sum = 100;

sum = sum + a;

return(sum);}

04/20/23 292

Output

When sum is auto• The I Value is:101• The I Value is:102• The I Value is:103• The I Value is:104• The I Value is:105• The I Value is:106• The I Value is:107• The I Value is:108• The I Value is:109• The I Value is:110

When sum is static• The I Value is:101• The I Value is:103• The I Value is:106• The I Value is:110• The I Value is:115• The I Value is:121• The I Value is:128• The I Value is:136• The I Value is:145• The I Value is:155

04/20/23 293

Register Variables

• The variables are declared using register keyword.• The scope and lifetime is same as that of automatic variables.• For any given operation the data available in the memory should be

transferred to the CPU registers.• So if the data are stored in register itself then the time for data

transfer from the memory to the register is saved.• Only a few values can be placed at a time and hence it is advisable

to use limited register variables. main(){ register int i; for(i=0;i<10;i++) printf(“%d”,i);}

04/20/23 294

External variables

• It refers to the location outside a block i.e., prior to the main() or beyond the closing braces ( } ) of the outermost block in a program .

• The value is available throughout the program because of its global scope.

• Whenever an external variable is modified in a block, the effect is propagated to all places where ever it is used.

04/20/23 295

Sample Program

main()

{

extern int x=5;

int y = 10,z;

z = y/x;

printf(“x = %d, y = %d, z = %d”, x, y, z);

}

C Standard Library

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C Standard Library

Every implementation of C comes with a standard library of predefined functions.

Note that, in programming, a library is a collection of functions.

The functions that are common to all versions of C are known as the C Standard Library.

04/20/23 298

C Standard Library Function ExamplesFunctionName

MathName Value Example

abs(x) absolute value

|x| abs(-1) returns 1

sqrt(x) square root x0.5 sqrt(2.0) returns 1.414…

exp(x) exponential ex exp(1.0) returns 2.718…

log(x) natural logarithm

ln x log(2.718…) returns 1.0

sin(x) sine sin x sin(3.14…) returns 0.0

cos(x) cosine cos x cos(3.14…) returns -1.0

tan(x) tangent tan x tan(3.14…) returns 0.0

ceil(x) ceiling┌ x ┐

ceil(2.5) returns 3.0

floor(x) floor└

x ┘

floor(2.5) returns 2.0

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Using the C Standard Math LibraryIf you’re going to use functions like cos that are from

the part of the C standard library that has to do with math, then you need to do two things:

1. In your source code, immediately below the#include <stdio.h>you must also put#include <math.h>

2. When you compile, you must append -lm to the end of your compile command: gcc -o funcargs funcargs.c –lm(Note that this is hyphen ell em, NOT hyphen one em.)

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UNIT VSTRUCTURES AND FILES

04/20/23 Lecture 2: User Defined Data Types

301

User Defined Data types

STRUCTURES

04/20/23 30204/20/23 Lecture 2: User Defined Data Types

302

User Defined Data types• C has several mechanisms for creating data types other

than the basic ones (int, float, etc.) provided by the language.

– structs – a collection of named variables– unions – a types that can hold one of a set of variables– enum – a set of named integers– typedef – define a name for a user type

• These tools are especially useful when combined with pointers and dynamic memory allocation.


303

Structure1. A structure is derived type usually representing a collection of

variables of same or different data types grouped together under a single name.

2. The variables or data items in a structure are called as members of the structure.

3. A structure may contain one or more integer variables, floating – point variables character variables, arrays, pointers , and even other structures can also be included as members.

4. Structures help to organize data, particularly in large programs, because they allow a group of related variables to be treated as a single unit.

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Why use structs?

• The last example is one of the main reasons. Rather than having four arrays of items, we have one array of structs.

• When combined with dynamic memory allocation, we can create many different data structures (trees, lists, heaps, etc.).

• Structs help to keep code organized logically.


305

Declaring a Structure

Structure declarations are somewhat more complex than array

declarations since a structure must be defined in terms of its individual

members.

The general form of the Structure is:

struct <structure_name>

{

data_type member_1;

data_type member_1;

…………………………..

…………………………..

data_type member_n;

};


306

Usually declare structs in global scope, often in a separate file.

// Declare a person struct

struct person { char name[50]; int age; char phone[15]; float height;};

1. struct is keyword.

2. Structure_name is the user defined name, usually referred as a tag, which is used to identify the structure.

3. Member_1 to Member_n is the list of members with its data type in structures.

4. The list of member declarations is enclosed in a pair of flower braces.

5. The closing brace of the structure and the semicolon ends the structure declaration.

Example:


307

• A field is an individual variable in the struct. It is accessed by var. field where var is the struct variable and field is the field name.

// Declare a person struct

struct person { char name[50]; int age; char phone[15]; float height;};

fields

tag name or structure name

•Each field has its own memory location.

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Various ways to create a structure

Defined for variables

struct Date { // see example: structEx2.c int month; int day;} birth, current;

struct Date { // see example: structEx1.c int month; int day;} ;

struct { // see example: structEx0.c int month; int day;} birth, current;

Defined as a new data type

Defined as both a new data type and variables


309

Defining a Structure1. Declaring a structure is just a skeleton it merely describes the template.

2. It does not reserve any memory space rather the declaration creates a new data type.

3. So, to use the structure you have to define it.

4. Defining a structure means creating variables to access the members in the structure.

5. Creating a structure variable allocates sufficient memory space to hold all the members of the structure.

6. The structure variables can be created during structure declaration or by explicitly using the structure name.

The general form of the Structure is:


{

data_type member_1;

data_type member_1;

…………………………..

…………………………..

data_type member_n;

}structure_variable;


310

struct person { char name[50]; int age[5]; char phone[15]; float height;}stud;

Example:

Where the structure person declares a variable stud of its type. The structure_variable is are declared like ordinary variables is used to access the members of the structure. More than one structure_variable can also be declared by placing a comma in between the variables.

The memory allocation for the structure person is

name 50 bytes

age 5 bytes

phone 15 bytes

height 4 bytes

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The syntax for defining the structure using the structure name is

Example:

struct person stud; or person stud;

If you need only one structure variable, the structure name or the tag is not necessary.

For example.struct{ char name[50]; int age[5]; char phone[15]; float height;}stud;

struct structure_name structure_variable;Or

structure_name structure_variable;

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1. Where the structure declares and defines a variable named stud.

2. Note that the structure name or the structure variables may be omitted, but both, should not be omitted.

3. The member names within a particular structure must be distinct from one another though a member name can be same as the name of the variable, which is defined outside the structure.

4. For example,

struct{ char name[50]; int age[5]; char phone[15]; float height;}stud;char phone[15];

1. Where character variable phone inside the structure shares the same name with the variable phone declare outside the structure.

2. Note that a structure declaration that is not followed by a list of variables reserves not storage space, it merely describes the template (i.e., the structure is only defined not declared.

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Accessing Structure Members

1. We have declared and defined the structure and how let us see how the elements of the structure can be accessed.

2. A member of a structure is always referred and accessed by the structure variable.

3. The general form or the syntax of accessing a member of a structure is

Example:

stud.name; stud.age; stud.phone stud.height

To assign a value to the member of the structure use,

stud.name = “sakthi vinayagam”; stud.age = “32”;

structure_variable.member_name;

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#include <stdio.h>

// Declare a person structstruct person{

char name[50];int age;char phone[15];float height;

};

int main() {

struct person stud;

stud.name = “sakthi”;stud.age = 32;stud.phone = “9865140132”;stud.height = 175.34;

Structs: Example

stud

sakthiname

31age

9865140132phone

175height

char[50]

int

char[15]

float

printf(“The Stud name is:%d\n”,stud.name);printf(“The Stud age is: %d\n”,stud.age);printf(“The Stud phone is:%d\n”,stud.phone);printf(“The Stud height is:%d\n”,stud.height);

getch();

}

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Initializing Structure1. The syntax of C language prevents the programmer from initializing individual

structure members within the structure template.

2. Structure members can be initialized only by using structure variables during structure declarations or by explicitly using the structure name.

3. The syntax for initializing the structure during structure declaration is


{

data_type member_1;

………………………..

data_type member_n;

}structure_variable = {value_1,value_2,……….value_n};

Example:

struct{ char name[50]; int age[5]; char phone[15]; float height;}stud = {“sakthi”,31,”986514013”,173.86};

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Example Program for structure initialization#include <stdio.h>

// Declare a person structStruct{ char name[50]; int age[5]; char phone[15]; float height;}stud = {“sakthi”,31,”986514013”,173.86};

int main(){ printf(“The Stud name is:%d\n”,stud.name); printf(“The Stud age is: %d\n”,stud.age); printf(“The Stud phone is:%d\n”,stud.phone); printf(“The Stud height is:%d\n”,stud.height);

getch();}

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#include <stdio.h>

// Declare a person structstruct person{

char name[50];int age;char phone[15];float height;

};

int main() { struct person stud_1={“sak”,31}; struct person stud_2={“vel”}; stud_1.phone = “9865140132”; stud_1.height = 175.34;

stud_3 = stud_1;

printf(“The Stud name is:%d\n”,stud_1.name);printf(“The Stud age is: %d\n”,stud_1.age);printf(“The Stud phone is:%d\n”,stud_1.phone);printf(“The Stud height is:%d\n”,stud_1.height);

printf(“The Stud name is:%d\n”,stud_2.name);

printf(“The Stud name is:%d\n”,stud_3.name);printf(“The Stud age is: %d\n”,stud_3.age);printf(“The Stud phone is:%d\n”,stud_3.phone);printf(“The Stud height is:%d\n”,stud_3.height);

getch();}

Note:

The information contained in one structure variable can also be assigned to another structure variable using a single assignment statement.

Example Program for structure initialization

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Sl.No. Array Structures

1. An array is an single entity representing a collection of data items of same data types.

A structure is a single entity representing a collection of data items of different data types.

2. Individual entries in an array are called elements.

Individual entries in a structure are called members.

3. An array declaration reserves enough memory space for its elements.

The structure definition reserves enough memory space for it s members.

4. No keyword is used to represent arrays except the square braces [] preceding the variable name indicates that it is an array.

The keyword struct tells us that we are dealing with structures.

5. Initialization of elements can be done during array declaration.

Initialization of members can be done only during structure definition.

Difference Between Array and Structure

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Difference Between Array and Structure Conti…

Sl.No. Array Structures

6. The elements of an array are stored in sequence of memory locations.

The members of a structure are not stored sequences of memory locations.

7. The array elements are accessed by its followed by the square braces [] within which the index is placed.

The members of a structure are accessed by the dot operator (also called as the period operator)

8. The General format is data_type variable_name [size];Ex: int sum [100];

The General format isstruct <struct_name>{ data_type structure_member_1; data_type structure_member_2; data_type structure_member_3;

. . data_type structure_member_n;}structure_variable;Ex:struct student{ char studentname[20]; int rollno;}stud;

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STRUCTURE WITHIN STRUCTURE OR NESTING OF STRUCTURE

1. Structure within a structure means nesting of structures.

Example:

struct salary

{

char name[20];

char department[10];

int basic_pay;

int dearness_allowance;

int house_rent_allowance;

int city_allowance;

}employee;

This structures defines name, department, basic pay and three kind of allowance. We can group all the items related to allowance together and declare them under a substructure.

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Case 1:

struct employee

{

char name[20];


struct salary

{

int basic_pay;



int city_allowance;

}emp_salary;

}emp_person;

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Case 2:

struct employee

{

char name[20];


};

struct salary

{

int basic_pay;



int city_allowance;

struct employee emp_persion;

}emp_salary;

Structures and Functions

There are three methods by which the values of a structure can be transferred from one function to another.

1. The first method is to pass each member of the structure as an actual argument of the function call. The actual arguments are then treated independently like ordinary variables. The is the most elementary method and becomes unmanageable and inefficient when the structure size is large.

2. The second method involves passing of a copy of the entire structure to the called function. Since the function is working on a copy of the structure, and changes to structure members within the function are not reflected in the original structure (in the calling function). It is , therefore, necessary for the function to return the entire structure back to the calling function. All Compilers may not support this method of passing the entire structure as a parameter.

3. The third approach employs a concept called pointers to pass the structure as an argument. In this case, the address location of the structure is passed to the called function. The function can access indirectly the entire structure and work on it. This is similar to the way arrays are passed to function. This method is more eifficient as compared to the second one.

The general format of sending a copy of a structure to the called function is:

function_name (structure_variable_name);

The called function takes the following form:

data_type function_name(struct_type st_name)

{

---------------

---------------

return (expression);

}

The following points are important to note:

1. The called function must be declared for its type, appropriate to the data type it is expected to return. For example, if it is returning a copy of the entire structure, then it must be declared as struct with an appropriate tag name.

2. The structure variable used as the actual argument and the corresponding formal argument in the called function must be of the same struct type.

3. The return statement is necessary only when the function is returning some data back to the calling function. The expression may be any simple variable or structure variable or an expression using simple variables.

4. When a function returns a structure, it must be assigned to a structure of identical type in the calling function.

5. The called functions must be declared in the calling function appropriately.

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We can send structures to functions

#include <stdio.h>struct Date{ int month; int day;} ;void callToFunction( struct Date val ); // function prototypeint main( ){ struct Date birth = {9, 31}; printf( "Birth date: %d/%d/\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d/\n", birth.month, birth.day );}void callToFunction( struct Date val ){ val.month = 1; val.day = 28;}

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#include <stdio.h>struct Date{ int month; int day;} ;void callToFunction( struct Date val ); // function prototypeint main( ){ struct Date birth = {9, 31}; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day );}void callToFunction( struct Date val ){ val.month = 1; val.day = 28;}


OUTPUT:cs157> gcc structFunc.ccs157> a.outBirth date: 9/31Birth date after function: 9/31

Function does not change original!

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#include <stdio.h>struct Date{ int month; int day;} ;void callToFunction( struct Date val ); // function prototypeint main( ){ struct Date birth = {9, 31}; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day );}void callToFunction( struct Date val ){ val.month = 1; val.day = 28;}


OUTPUT:cs157> gcc structFunc.ccs157> a.outBirth date: 9/31Birth date after function: 9/31

Function does not change original!

Val is a full copy of birth

structure

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#include <stdio.h>struct Date{ int month; int day;} birth = {9, 31};

void callToFunction( );

int main( ){ printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( ); printf( "Birth date after call to function: %d/%d\n", birth.month, birth.day );}void callToFunction( ){ birth.month = 1; birth.day = 28;}

We can refer to globally defined structures

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#include <stdio.h>struct Date{ int month; int day;} birth = {9, 31};

void callToFunction( );

int main( ){ printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( ); printf( "Birth date after call to function: %d/%d\n", birth.month, birth.day );}void callToFunction( ){ birth.month = 1; birth.day = 28;}

We can refer to globally defined structures

OUTPUT:cs157> gcc structFunc2.ccs157> a.outBirth date: 9/31Birth date after function: 1/28

Function does

change original!

birth is a global variable, so function

affects original

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#include <stdio.h>struct Date{ int month; int day;};void callToFunction( struct Date * );int main( ){ struct Date birth; birth.month = 9; birth.day = 31; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( &birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day );}void callToFunction( struct Date *birth ){ birth->month = 1; birth->day = 28;}

We can send a pointer to the structure

Use -> to dereference from a

pointer

Send the address to the function

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#include <stdio.h>struct Date{ int month; int day;};void callToFunction( struct Date * );int main( ){ struct Date birth; birth.month = 9; birth.day = 31; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( &birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day );}void callToFunction( struct Date *birth ){ birth->month = 1; birth->day = 28;}

We can send a pointer to the structure

OUTPUT:cs157> gcc structFunc3.ccs157> a.outBirth date: 9/31Birth date after function: 1/28

Function does

change original!

Use -> to dereference from a

pointer

Send the address to the function

Arrays of Structures

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We use structures to describe the format of a number of related variables. For example, in analyzing the marks obtained by a class of students, we may use a template to describe student name and marks obtained in various subjects and then declare all the student as structure variables. In such cases, we may declare an array of structures, each element of the array representing a structure variable.

For example:

struct class student [100];

defines an array called student, that consists of 100 elements. Each element is defined to be of the type struct class. Consider the following declaration:

struct marks

{

int subject_1;int subject_2;int subject_3;

}

main

{

struct marks student [3] =

{{45,68,81},{75,53,69},{57,36,71}};

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We can create arrays of structs just like any other type.name

age

phone

4.21height

char[50]

unsigned char

char[15]

float

int main() { struct person people[4]; people[2].age = 54; people[0].height = 4.21; ...etc...}

name

age

phone

height

char[50]

unsigned char

char[15]

float

name

54age

phone

height

char[50]

unsigned char

char[15]

float

name

age

phone

height

char[50]

unsigned char

char[15]

float

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#include <stdio.h>#include <string.h>struct student { char name[50]; int age; char phone[15]; float height;};#define NUMSTUDENTS 3int main( ){ struct student cs157[NUMSTUDENTS] =

{ {"Bob", 84, "555-1010", 6.3 }, { "Rob", 14, "555-1100", 4.8 }, { "Zob", 4, "555-9999", 2.7 }, } ; for( int i=0; i<NUMSTUDENTS; i++ ) printf( "Student %i: %s %d years old\n", i+1, cs157[i].name, cs157[i].age );}

OUTPUT:cs157> gcc people.c -std=c99cs157> a.outStudent 1: Bob 84 years oldStudent 2: Rob 14 years oldStudent 3: Zob 4 years old

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Structures and sizeof• Due to memory alignment restrictions, the size of a structure is >= the sum

of the sizes of its member variables

struct blah {char x;

int y;

char z;

};

• Always use sizeof to determine the size of a structure• sizeof(blah) 12 bytes

x

y y y y

z

= Padding

Memory layout

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C Permits the use of arrays as structure members. We can use single – or multi – dimensional array of type int or float.

For Example, the following structure declaration is valid:

struct marks

{

int number;

float subject [3];

} student [2];

Here the member subject contains three elements, subject [0], subject [1] and subject [2]. These elements can be accessed using appropriate subscripts.

For example, the name

student [1] . Subject [2];

Would refer to the marks obtained in the third subject by the second student.

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Structure bit fields• Recall bit flags and bit masks• Useful when we need to pack several flags or objects into the

smallest amount of space possible• Structure bit fields make this a little easier at the cost of portability

struct argb {unsigned int alpha : 8;unsigned int red : 8;unsigned int green : 8;unsigned int blue : 8;

};

• Implementation-dependent!

Unions

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Unions

• A union is a type that allows several variables to be stored in the same memory location (but not at the same time).

• It provides a way of improving memory efficiency.

• On most modern desktop machines, this is not really an issue, and unions will be used less frequently.

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// Declare a union

union int_or_float { int i; float f;};

Unions

• The declaration is similar to that of a struct, but the implementation is different.

• Only one field will contain data and be accessible at any given time.

tag name

fields

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// Declare a union


Unionstag name

fields

q

14????

i

f

int

float

int main() { union int_or_float q; q.i = 14;

}

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// Declare a union


Unionstag name

fields

q

????175.543

i

f

int

float

int main() { union int_or_float q; q.i = 14; q.f = 175.543;

}

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// Declare a union


Unionstag name

fields

q

175????

i

f

int

float

int main() { union int_or_float q; q.i = 14; q.f = 175.543; q.i = q.f;}

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Unions

• Accessing a union member that has not been assigned most recently will produce undefined results.

• Unless you are really concerned about memory use (perhaps when writing code for an embedded device), stay away from unions.

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Unions• Syntactically similar to structures• However, all member variables occupy the

same location in memory• You are responsible for accessing the right

members at the right time• Union size is size of the largest member

union UBlah {char x;int y;char z;

};

x,y,z

Memory layout

y y y

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Unions (2)union {char x;int y;char* z;

} utype;

utype.x = 'c';printf("%c\n", utype.x);utype.z = "Hello";printf("%s\n", utype.z);printf("%d\n", utype.y); /* Undefined! */

Enumerated Types

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Enumerated Types

• The enum type allows you to specify a finite set of names to which C will automatically give values.

• These names can be compared which makes them useful in situations where a variable should only take on values from a small set.

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Enum// Declare a enum

enum r_p_s { rock, paper, scissors};

tag name

values

• Values are assigned starting at zero and incrementing by 1.

• While enums are comparable with ints, you should avoid treating them as integers.

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enum Example

// Declare a enum


player

int main() { enum r_p_s player, machine;

}

machine

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enum Example

// Declare a enum


player

rock

int main() { enum r_p_s player, machine; player = rock;

}

machine

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enum Example// Declare a enum

enum r_p_s { rock, paper, scissors};player

rockint main() { enum r_p_s player, machine; player = rock; machine = scissors;

if (machine == player)printf(“Tied.\n”);

else...

}

machine

scissors

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enumerated types example

// Declare a enum


player

rock

enum result happened = tie;

if(machine == player) happened = tie;else if((machine+1)%3 == player) happened = win; else if((player+1)%3 == machine) happened = loss;

machine

scissors

// Declare a enum

enum result { win, loss, tie};

happened

win

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Tag Names and Declarations• The syntax for defining structs, unions, and

enums is very similar.

• The type is either struct, unions, or enums.

• The tag is a name for the type. It differentiates on struct from another.

• After the declaration a list of variables to create can be given.

type tag { ...} var1, var2, var3, ...;

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typedefs

• Allow you to make a new “logical”name for an existing data type.

• Like a name-tag

• Makes code more readable.

typedef char * string;

int main ( ) {

// instead of char* my_string; string name; strcpy(name,”hello”);}

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Typedefs

• A typedef is a name for some type. Any type can be named with a typedef.

struct my_struct_S {

int age;char name[30];

};

typedef struct my_struct_S person;

int main(){

// instead of struct my_struct_S people[20];person people[20];

}

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Typedefs• For stucts, enums, and unions the syntax can be

slightly simplified.

• We can combine the declaration and the typedef. This allows us to leave out the tag name.

typedef struct {

int age;char name[30];

} person;

int main( ){

person people[20]; }

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Initialization of User Defined Types

• We can define the values of user defined types at the declaration. The syntax is similar to that of array intialization.

typedef struct { char name[50]; unsigned char age; char phone[15]; float height;} person;

int main() { person company[2] = {{“Robert Smitherson”, 45, “(303)-111-2222”, 5.9}, {“Sally Robertson”, 38, “(303)-222-1111”, 5.5}};}

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Nested Types

• It is legal to nest the definition of user defined types. Structs, for example, can have structs (or unions or enums) as members.

• The members of nested types are accessed using the same ‘.’ operator. We might, for example, have something like var.stype.age.

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Nested User Defined Types

typedef struct { char name[50]; unsigned char age; char phone[15]; float height; union { int num_new_teeth; // if age <= 2 int school_grade; // if age <= 18 int fake_hips; // if age >= 60 } info;} person;

int main() { person bob; bob.age = 75; bob.info.fake_hips = 2;}

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Anonymous Nested Types

• You can leave off the type name for nested types.

typedef struct { unsigned char age; union { int num_new_teeth; // if age <= 2 int school_grade; // if age <= 18 int fake_hips; // if age >= 60 }; //no name} person;

int main() { person bob; bob.age = 75; bob.fake_hips = 2;}

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Complex exampletypedef struct { enum { beverage, candy, snack } type; char name[30]; union { float fl_ounces; int pieces; int servings; }; float cost; int count;} item;

int main() { item vendmach[20]; ...

vendmach[0].type = beverage;strcpy(vendmach[0].name,”Coke”);vendmach[0].fl_ounces = 12;vendmach[0].cost = 1.25;vendmach[0].count = 10;

vendmach[0].type = candy;strcpy(vendmach[0].name,”KitKat”);vendmach[0].pieces = 4;vendmach[0].cost = 0.95;vendmach[0].count = 7;

vendmach[0].type = snack;strcpy(vendmach[0].name,”Pringles”);vendmach[0].servings = 2;vendmach[0].cost = 1.10;vendmach[0].count = 5;

...

FILE HANDLING IN C

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Files in C

• In C, each file is simply a sequential stream of bytes. C imposes no structure on a file.

• A file must first be opened properly before it can be accessed for reading or writing. When a file is opened, a stream is associated with the file.

• Successfully opening a file returns a pointer to (i.e., the address of) a file structure, which contains a file descriptor and a file control block.

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Files in C • The statement:

FILE *fptr1, *fptr2 ;

• declares that fptr1 and fptr2 are pointer variables of type FILE. They will be assigned the address of a file descriptor, that is, an area of memory that will be associated with an input or output stream.

• Whenever you are to read from or write to the file, you must first open the file and assign the address of its file descriptor (or structure) to the file pointer variable.

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Opening Files• The statement:

fptr1 = fopen ( "mydata", "r" ) ;

would open the file mydata for input (reading).

• The statement:

fptr2 = fopen ("results", "w" ) ;

would open the file results for output (writing).

• Once the files are open, they stay open until you close them or end the program (which will close all files.)

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Modes for opening files

• The second argument of fopen is the mode in which we open the file. There are three

• "r" opens a file for reading• "w" opens a file for writing - and writes over all previous

contents (deletes the file so be careful!)• "a" opens a file for appending - writing on the end of the

file.

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The exit() function• Sometimes error checking means we want an

"emergency exit" from a program. We want it to stop dead.

• In main we can use "return" to stop.• In functions we can use exit to do this.• Exit is part of the stdlib.h library• exit(-1);• in a function is exactly the same as• return -1;• in the main routine

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Testing for Successful Open• If the file was not able to be opened, then the value

returned by the fopen routine is NULL.

• For example, let's assume that the file mydata does not exist. Then:

FILE *fptr1 ;

fptr1 = fopen ( "mydata", "r") ;

if (fptr1 == NULL)

{

printf ("File 'mydata' did not open.\n") ;

}

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Reading From Files• In the following segment of C language code:

int a, b ;FILE *fptr1, *fptr2 ;fptr1 = fopen ( "mydata", "r" ) ;fscanf ( fptr1, "%d%d", &a, &b) ;

• the fscanf function would read values from the file "pointed" to by fptr1 and assign those values to a and b.

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End of File• The end-of-file indicator informs the program when there are

no more data (no more bytes) to be processed.• There are a number of ways to test for the end-of-file

condition. One is to use the feof function which returns a true or false condition:

fscanf (fptr1, "%d", &var) ;

if ( feof (fptr1) )

{

printf ("End-of-file encountered.\n”);

}

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End of File• There are a number of ways to test for the end-of-file

condition. Another way is to use the value returned by the fscanf function:

int istatus ;

istatus = fscanf (fptr1, "%d", &var) ;

if ( istatus == EOF )

{

printf ("End-of-file encountered.\n”) ;

}

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Writing To Files• Likewise in a similar way, in the following segment of C

language code:

int a = 5, b = 20 ;

FILE *fptr2 ;

fptr2 = fopen ( "results", "w" ) ;

fprintf ( fptr2, "%d %d\n", a, b ) ;

• the fprintf functions would write the values stored in a and b to the file "pointed" to by fptr2.

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Closing Files

• The statements:

fclose ( fptr1 ) ;fclose ( fptr2 ) ;

• will close the files and release the file descriptor space and

I/O buffer memory.

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Reading and Writing Files#include <stdio.h>int main ( ){

FILE *outfile, *infile ;

int b = 5, f ;float a = 13.72, c = 6.68, e, g ;

outfile = fopen ("testdata", "w") ;fprintf (outfile, "%6.2f%2d%5.2f", a, b, c) ;fclose (outfile) ;

infile = fopen ("testdata", "r") ;fscanf (infile,"%f %d %f", &e, &f, &g) ;printf ("%6.2f%2d%5.2f\n", a, b, c) ;printf ("%6.2f,%2d,%5.2f\n", e, f, g) ;

}

12345678901234567890**************************** 13.72 5 6.68 13.72, 5, 6.68

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Thank You!

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