1 review of chapter 6: the fundamental data types

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Review of Chapter 6:

The Fundamental Data Types

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Declarations All variables must be declared before they

can be used.Tell the compiler to set aside an

appropriate amount of space in memory to hold values of variables.

Different machine instructions are used when an operator applied on different data typesDeclarations enable the compiler to instruct the machine to perform specified operations correctly.

Declarations and Expressions Declarations:

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Expressions Meaningful combinations of

constants, variables, and function calls. Most expressions have both a value and a

type Examples:

Declarations: int a =12, b=10, c, d;Function min(int x, int y) exp1, function call min(var1, var2): min(a,b) exp2, var * constant: a*12 exp3, function call min(exp1, exp2): min(min(a,b),

a*12)

Declarations and Expressions Declarations:

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Integral types The types that can be used to hold integer

values.Characters: char, signed char, unsigned char short, int, long, unsigned short, unsigned, unsigned long

Floating types The types that can be used to hold real values.

float, double, long double

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Characters and the data Type char

Characters: Each char is stored in one byte of memory Variables of any integral type can be used to

represent characters.char, int

When a variable is used to read in characters and a test must be must be made for EOF,

while ((c=getchar())!=EOF){ putchar(c);}

The variable should be of type int, not char

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The Data Type int and the integral types

short, int, long storage provided for each type:

short <= int <= long

signed/unsigned The integer values stored in an unsigned

variable have no sign. Example, If a variable of type unsigned int is

stored in 4 bytes,Range of unsigned: 0, 1, ……, 232-1 Range of int: -231, ……, -2, -1, 0, 1, 2, ……,

231-1

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The sizeof Operatorsizeof(object)

Returns an integer that represents the number of bytes needed to store the object in memory.

An object can be a type, sizeof(int)an expression, sizeof(a+b)an array or structure type (introduced later)

sizeof(….) is an operator, not a functionIf sizeof is being applied to a type,

parentheses are required, o example: sizeof(int)

Otherwise, parentheses are optional,o example: sizeof a+b

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Mathematical Functions

Mathematical Functions There are no built-in mathematical functions

in C language Functions are available in the mathematics

library. How to use the functions in the

mathematics library?In the code: #include <math.h>Compile: gcc –lm f.c

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Conversions and Casts

Conversions and Casts Conversions can occur when the operands

of a binary operator are evaluated.Example: int i, float f;

expression i+fo i is promoted to a float o The expression i+f as a whole has type float.

Cast operator (type)Example:

int a; double b;b = (double) a;

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Chapter 8

Functions, Pointers, and Storage Classes

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Introduction

Declarations tell the compiler to set aside an appropriate amount of space in memory to hold values associated with variables.

Question: Write a code to check the memory allocated to a variable?

The address of the memory allocated to the variable.

The size of the memory allocated to the variable.

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Introduction

#include <stdio.h>int main(void){ int a, b; /************************************************ print out the address and size of memory allocated to a ************************************************/

/************************************************ print out the address and size of memory allocated to b ************************************************/}

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Given a variable a, how to check the memory allocated to a?

The address of the memory allocated to a.

The size of the memory allocated to a.

Introduction

Example: scanf(“%d”, &a);%d: format&a: the address of variable a

Address operator: &a

sizeof(a): returns an integer that represents the number of bytes needed to store variable a in memory.

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Introduction#include <stdio.h>int main(void){ int a,b; /* print out address and size of memory allocated to a */

/*print out address and size of memory allocated to b */

}

printf("[int a] address: %u, size: %d\n", &a, sizeof(a));

printf("[int b] address: %u, size: %d\n", &b, sizeof(b));

% a.out[int a] address: 4290705268, size: 4[int b] address: 4290705264, size: 4

Memory

42907052714290705270429070526942907052684290705267429070526642907052654290705264429070526342907052624290705261

address

a

b

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Introduction#include <stdio.h>int main(void){ int a,b; /* print out address and size of memory allocated to a */


}

printf("[int a] address: %u, size: %d\n", &a, sizeof(a));

printf("[int b] address: %u, size: %d\n", &b, sizeof(b));

Can we use a variable p to store the address, such as &a and &b?

If yes, how?What is the data type of p?How to declare variable p?How to assign an address to p?How to get the value at the address stored in p? Yes, pointer

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Outline

PointerPointers to voidCall-by-ReferenceScope RulesStorage ClassesStatic External VariablesDefault InitializationFunction Declarations and DefinitionsThe Type Qualifiers const and volatile

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Pointer

Pointers: Pointer variables can be declared in programs and

then used to take addresses as values Example:

int *p; int i;declares p to be type “pointer to int”:

o the address stored in p is an address to an int variable

p = &i;o The compiler decides what address to use to store

the value of the variable i.o p contains the address of i; p points to i,

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Pointer#include <stdio.h>int main(void){ int a,b; /* print out address and size of memory allocated to a */


}

printf("[int a] address: %p, size: %u\n", &a, sizeof(a));

printf("[int b] address: %p, size: %u\n", &b, sizeof(b));


If yes, how?What is the data type of p?How to declare variable p?How to assign an address to p?How to get the value at the address stored in p?

pointer

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Pointer

How to declare a pointer?

Examples: int *pi1, *pi2, i;

o pi1: a pointer to into pi2: a pointer to into i: int

How to declare a pointer named pb to double?double *pb;

DataType *pointer1, *pointer2;

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Pointer

How to assign address to a pointer?

where address can be the address of a variable or another pointer.

int *pi1, *pi2, i; pi1 = &i;

/* pi1 contains the address of variable i */ /* pi1 points to i */ pi2 = pi1; /* pi2 is assigned the value of pi1,

*/ /* that is, the address of variable i */ /* pi2 points to i */

pointer = address;

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#include<stdio.h>int main(){ int *pi1, *pi2, i; pi1 = &i; /* pi1 points to i */ pi2 = pi1; /* pi2 points to i */ i = 5; printf("%d %d %d\n", i, *pi1, *pi2);}

Pointer

How to access the value stored at the address contained in a pointer?Dereference, or indirection, Operator *

o *p returns the value of the variable to which p points

*pointer

*pi1: the value of the variable to which pi1 points

*pi2: the value of the variable to which pi2 points

% a.out5 5 5

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Pointer#include <stdio.h>int main(void){ int a,b; /* print out address and size of memory allocated to a */


}

printf("[int a] address: %p, size: %u\n", &a, sizeof(a));

printf("[int b] address: %p, size: %u\n", &b, sizeof(b));


If yes, how?What is the data type of p?How to declare the p?How to store the address in p?How to get the value located at the address stored p?

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Pointer#include <stdio.h>int main(void){ int a =1,b =2; int *pa, *pb; pa = &a; pb = &b; printf("[int a] address: %u, value: %d \n", pa, *pa); printf("[int b] address: %u, value: %d \n", pb, *pb);} %a.out

[int a] address: 4290705268, value: 1[int b] address: 4290705264, value: 2

Declaration of a pointer: DataType *pointer; Assign address to a pointer: pointer = address;Access the value of the variable to which the pointer points: *pointer

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Pointer

Pointers: Pointer variables can be declared in programs

and then used to take addresses as valuesDeclaration

o DataType *pointer1, *pointer2; double *pb, x;

Assignmento pointer = address;

pb = &x;Dereferencing

o Access the value of the variable to which the pointer points by dereference operator *: *pointer

*pb = 3; What is the value of x?

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Pointer

Pointers: What is the legal range of values of any

pointer?a set of positive integers that are interpreted as

machine addresses on a particular C system, andthe special address 0

o stdio.h: #define NULL 0o NULL can be used to represent false

while(NULL) printf(“loop\n”);

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#include <stdio.h>int main(void){ int a, b; int *p; printf("Memory Allocation:\n"); printf("[a]: Addr=%u, Size=%d\n", &a, sizeof(a)); printf("[b]: Addr=%u, Size=%d\n", &b, sizeof(b)); printf("[p]: Addr=%u, Size=%d\n", &p, sizeof(p)); a = b = 7; p = &a; printf("*p = %d\n", *p); *p = 3; printf("a = %d\n", a); p = &b; *p = 2 * *p - a; printf("b = %d\n", b); p = &a; printf("Input an integer: "); scanf("%d", p);}

% a.outMemory Allocation:[a]: Addr=4290705268, Size=4[b]: Addr=4290705264, Size=4[p]: Addr=4290705260, Size=4

4290705268

4290705264

4290705260

addressMemory

a

b

p

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4290705268

4290705264

4290705260

addressMemory

a

b

p

% a.outMemory Allocation:[a]: Addr=4290705268, Size=4[b]: Addr=4290705264, Size=4[p]: Addr=4290705260, Size=4*p = 7

7

7

4290705268

*p: the value of the variable to which p

points

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4290705268

4290705264

4290705260

addressMemory

a

b

p

% a.outMemory Allocation:[a]: Addr=4290705268, Size=4[b]: Addr=4290705264, Size=4[p]: Addr=4290705260, Size=4*p = 7a = 3

7

7

4290705268


points

3

31


4290705268

4290705264

4290705260

addressMemory

a

b

p

% a.outMemory Allocation:[a]: Addr=4290705268, Size=4[b]: Addr=4290705264, Size=4[p]: Addr=4290705260, Size=4*p = 7a = 3b = 11

7

7

4290705268


points

3

4290705264

11

32

4290705264


4290705268

4290705264

4290705260

addressMemory

a

b

p

% a.outMemory Allocation:[a]: Addr=4290705268, Size=4[b]: Addr=4290705264, Size=4[p]: Addr=4290705260, Size=4*p = 7a = 3b = 11Input an integer:

7

7

4290705268

3

11

2

scanf(format, addr): the input is placed at the address specified by addr.

2

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Pointer

Summary Pointer variables can be declared in

programs and then used to take addresses as values

Legal range of values of any pointer:a set of positive integers that are interpreted as

machine addresses andthe special address NULL.

o stdio.h: #define NULL 0

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Pointer

Summary (cont’d) Declaration: dataType *pointer1, *pointer2;

double *pb, x; Assignment: pointer = address;

pb = &x; Addressing: a pointer can be used in a place

where address occursscanf(“%d”, p);

Dereferencing: access the value of the variable to which the pointer points by *: *pointer*p = 3;

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Outline


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Pointers to void

In ANSI C, one pointer can be assigned to another only when

they both have the same type, or when one of them is of type pointer to void

void * can be considered as a generic pointer type NULL can be assigned to any pointer.

Example:int *p;double *q;void *v;p = 0;p = NULL;p = (int *) 1;p = v = (int *) q;p = q;p =1;

/* legal *//* legal *//* legal *//* legal *//* illegal *//* illegal */

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Outline


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Call-by-Reference

Call-by-value Function Invocation

fun_name(exp1, exp2); All arguments are passed call-by-value

Each argument is evaluated, and its value is used locally in place of the corresponding formal parameter.

If a variable is passed to a function, the stored value of that variable in the calling environment is not changed.

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Call-by-Reference#include <stdio.h>void swap(int, int);int main(void){ int a=3, b=7; printf("main: %d %d\n", a, b); swap(a,b); printf("main: %d %d\n", a, b); return 0;}void swap(int a, int b){ int tmp; tmp = a; a = b; b = tmp; printf("swap: %d %d\n", a, b);}

% a.outmain: 3 7swap: 7 3main: 3 7

Memory

a

b 7

3

swap: a

swap: b

swap: tmp

7

3

3

7

3

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Call-by-Reference#include <stdio.h>void swap(int* , int* );int main(void){ int a=3, b=7; printf("Addr %u, %u\n", &a,&b); printf("main: %d %d\n", a, b); swap(&a,&b); printf("main: %d %d\n", a, b); return 0;}void swap(int *a, int *b){ int tmp; tmp = *a; *a = *b; *b = tmp; printf("swap: %d %d\n", *a, *b);}

% a.outAddr 4290705268, 4290705264main: 3 7swap: 7 3main: 7 3

Memory

a

b 7

3

swap: a

swap: b

swap: tmp 3

4290705268

4290705264

4290705268

4290705264

7

3

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Call-by-Reference

Call-by-reference How to modify the values of the variables

referred to in the argument list?Declaring a function parameter to be a

pointerUsing the pointer in the function bodyPassing an address as an argument when

the function is called

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Call-by-Reference#include <stdio.h>void swap(int* , int* );int main(void){ int a=3, b=7; printf("Addr %u, %u\n", &a,&b); printf("main: %d %d\n", a, b); swap(&a,&b); printf("main: %d %d\n", a, b); return 0;}void swap(int *a, int *b){ int tmp; tmp = *a; *a = *b; *b = tmp; printf("swap: %d %d\n", *a, *b);}

How to modify the values of the variables referred to in the argument list?

Declaring a function parameter to be a pointerUsing the pointer in the function bodyPassing an address as an argument when the function is called

1 review of chapter 6: the fundamental data types

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