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COMP 111 – PROGRAMMING I

ASSIGNMENT, FORMATTING, AND INTERACTIVE INPUT

Instructor: Dr Dionysiou

ADMINISTRATIVE

! This week’s lecture !  [BRON06] Chapter 3 (3.1-3.5)

!  Assignment operations, formatting output, math functions, input operation, symbolic constants

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LECTURE OUTLINE

! Assignment Operations ! Mathematical Library Functions !  Input Operation ! Symbolic Constants ! Formatting Output

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ASSIGNMENT EXPRESSION

variableName = expression;

Assignment Operator

Lower precedence than any other arithmetic operator

Variable name

Expression Combination of constants, variables, functions that are evaluated to yield a result

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ASSIGNMENT EXPRESSION (CONT.)

num1 = 45;

num1

1652

num2

2222

A

2260

num1 is assigned the value 45

Steps: 1.  Evaluate the value of the

operand to the right of the assignment operator

2.  Store (assign) that value in the memory location associated with the variable to the left of the assignment operator

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num1 = 45;

45

num1

1652

num2

2222

A

2260

what happens if we now execute the statement num1 = 25;

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num1 = 45;

num1 = 25;

25

num1

1652

num2

2222

A

2260

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num1 = 15 + num2 * 2;

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num1

1652 3

num2

2222

A

2260

Consider the above memory configuration. What happens if we now execute the statement:

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num1 = 15 + num2 * 2;

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num1

1652 3

num2

2222

A

2260


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num1 = num2 + A;

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num1

1652 2

num2

2222

A

2260


No initial value! !!

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Draw the memory contents every time they change during the runtime execution of this program.

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What happens when a variable does not have a value? 13

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ASSIGNMENT EXPRESSION – ASSIGNMENT OPERATOR

! An assignment expression has a value! !  Value of the assignment expression is the same as the

contents of the variable on the left

cout << “The value of the expression is “ << (num1 = 5+7);

Output will be

The value of the expression is 12

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ASSIGNMENT EXPRESSION – ASSIGNMENT OPERATOR

! Equal sign (=) is the assignment operator !  Lower precedence than any other arithmetic operator

! Multiple assignments are possible !  It has right-to-left associativity

num1 = 45; num2 = 25;

num1 = num2 = 45;

num1 = (num2 = 45) is evaluated in this order: 1.  Assign 45 to num2 2.  Assign the result of the assignment statement

(num2 = 45) to num1

num2 = 45; num1 = num2;

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ASSIGNMENT EXPRESSION - COERCION

! Data type conversions take place across assignment operators

! Coercion !  Value assigned to variable on left of assignment operator

forced into data type of variable it is assigned to !  Integer value assigned to real variable !  Real value assigned to integer variable !  Pay attention to mixed-mode expressions!!

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ASSIGNMENT EXPRESSION – COERCION

Explain the output of this program.

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ASSIGNMENT EXPRESSION – COERCION

What is the output?

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ASSIGNMENT EXPRESSION – MORE EXPRESSIONS!

num1 = num1 + 5;

10

num1

1652

num2

2222

A

2260

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ASSIGNMENT EXPRESSION – MORE EXPRESSIONS!

num1 = num1 + 5;

10 15

num1

1652

num2

2222

A

2260

num1 is assigned the value 15

Steps: 1.  Evaluate the value of the operand to

the right of the assignment operator num1 + 5 10 + 5 15

2.  Store (assign) that value in the memory location associated with the variable to the left of the assignment operator

Overwrite whatever is in num1 by 15 20

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ASSIGNMENT EXPRESSIONS – MORE EXPRESSIONS!

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ASSIGNMENT EXPRESSIONS – MORE EXPRESSIONS!

! Assignment expressions that use the same variable on both sides of the operator may be written using shortcut assignment operators

+= -= *= /= %=

Complete expression Using shortcut assignment operator

sum = sum +5; sum += 5;

sum = sum - 5; sum -= 5;

sum = sum * (5 + num); sum *= 5 + num;

sum = 2 * (sum + num); cannot use it!

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ASSIGNMENT EXPRESSION – ACCUMULATING

!  Assignment statement of the form !  sum = sum + 10; !  sum += 10;

!  Accumulating subtotals !  Useful with repetition statement (chapter 5)

sum = 0; cout << “The value of sum is “ << sum << endl;

sum = sum + 10; cout << “The value of sum is “ << sum << endl;

sum +=100; cout << “The value of sum is “ << sum << endl;

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ASSIGNMENT EXPRESSION – COUNTING

!  Assignment statement of the form !  i = i + 1; !  count += 2;

!  The value of the variable is increased by a fixed amount !  Also useful with repetition statement (chapter 5)

count = 0; cout << “The value of count is “ << count << endl;

count = count + 1; cout << “The value of count is “ << count << endl;

count = count + 1; cout << “The value of count is “ << count << endl;

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ASSIGNMENT EXPRESSIONS – INCREMENT OPERATOR

! C++ provides the unary increment operator !  Increase the value by 1

variable++; (postfix increment) ++variable; (prefix increment)

Expression Alternative

i= i + 1 i++ or ++i

n= n + 1 n++ or ++n

count= count + 1 count++ or ++count

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ASSIGNMENT EXPRESSIONS – INCREMENT OPERATOR

!  Is there a difference between postfix and prefix increment operator? !  Yes, when the variable being incremented is used in an

assignment statement

n = n + 1; // increment n first k = ++n; k = n; // assign n’s value to k

k = n; // assign n’s value to k k = n++; n = n + 1; // and then increment n

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ASSIGNMENT EXPRESSIONS – DECREMENT OPERATOR

! C++ provides the unary decrement operator !  Decrease the value by 1

variable--; (postfix decrement) --variable; (prefix decrement)

Expression Alternative

i= i - 1 i--or --i

n= n - 1 n-- or --n

count= count - 1 count-- or --count

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ASSIGNMENT EXPRESSIONS – DECREMENT OPERATOR

!  Is there a difference between postfix and prefix decrement operator? !  Yes, when the variable being decremented is used in an

assignment statement

n = n - 1; // decrement n first k = --n; k = n; // assign n’s value to k

k = n; // assign n’s value to k k = n--; n = n - 1; // and then decrement n

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IN-CLASS EXERCISE

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IN-CLASS EXERCISE

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LECTURE OUTLINE


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USING MATH LIBRARY FUNCTIONS

! Advanced mathematical operations provided via standard pre-programmed functions !  e.g. trigonometric operations, square root, square

! Before using, you need to know: !  name of desired mathematical function !  what the mathematical function does !  type of data required by the function !  data type of result returned by the function !  how to include the library

!  #include<cmath>

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USING MATH LIBRARY FUNCTIONS (CONT.)

functionname (arguments)

We want to calculate the square root of integer value 123 1.  call math function that performs the calculation

sqrt(123);

2.  Display the returned value cout << “The square root of 123 is “ << sqrt(123) << endl;

Returned value

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Example Returned value

sqrt(123) 11.0905

sqrt(100 + 23) 11.0905

abs(-3) 3

pow(2.0, 5.) 32

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We want to calculate the expression 4 * sqrt(4.5 * 10.0 – 9.0) – 2.0

STEPS 1. Perform multiplication in the function argument

4 * sqrt(45– 9.0) – 2.0 2. Complete argument calculation

4 * sqrt(36.0) – 2.0 3. Return function value

4 * 6.0 – 2.0 4. Perform multiplication

24.0 – 2.0 5. Perform subtraction

22.0

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USING MATH LIBRARY FUNCTIONS - CASTING

!  Implicit casting !  Automatically made with

mixed expressions !  E.g. assigning a real

number to an int variable !  Result is ??

! Explicit casting !  Forcing the conversion of

a value to another type

static_cast <datatype> (expression);

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LECTURE OUTLINE


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INTERACTIVE INPUT

cin object enter data into a program during runtime

cout object display data from a program during runtime

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INTERACTIVE INPUT – cin

! Programs that do same calculation on same set of numbers every time not very useful

!  cin object !  Used to enter data into program while executing

!  (“get from”) operator, >> !  cin object puts computer into temporary pause state until user

types a value

! Always use a prompt !  String telling person at terminal what should be typed

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! Any number of values can be input using single cin statement !  cin extraction operation able to make some data type

conversions

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Debug once ! Run everywhere!

Test it on different platforms! 44

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LECTURE OUTLINE


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SYMBOLIC CONSTANTS

! Literal data !  Data explicitly identifying themselves

! Magic numbers !  Numbers used repeatedly in program

!  Potential source of error if constant must change

! Can give constants symbolic name !  Symbolic constants or named constants

!  const declaration qualifier

!  Value change need only be made once

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SYMBOLIC CONSTANTS (CONT.)

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PLACEMENT OF STATEMENTS

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LECTURE OUTLINE


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FORMATTING NUMBERS FOR OUTPUT

!  Important for program to present results attractively

!  iomanip header file must be included when manipulator requiring an argument is used

#include<iomanip>

! Parameterized manipulator !  Manipulator method that uses arguments

cout.setprecision( n ); // Where n can be any number

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FORMATTING NUMBERS FOR OUTPUT (CONT.)

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Must include iomanip

Two decimal digits

Do not use e notation

The width of the next “field”

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