Subject : Structured Programming Approach

Title : Pointers and Files

Difficulty : Medium

Pointer: A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before using it to store any variable address. The general form of a pointer variable declaration is −type *var-name;

Uses of pointer:

1.Pointers reduce the length and complexity of a program.

2.They increase execution speed.

3.A pointer enables us to access a variable that is defined outside the function.

4.Pointers are more efficient in handling the data tables.

5.The use of a pointer array of character strings results in saving of data storage space in memory.

Array of Pointers: Just like we can declare an array of int, float or char etc, we can also declare an array of pointers, here is the syntax to do the same.

Syntax:

datatype *array_name[size];

Example:

int *arrop[5];

Here arrop is an array of 5 integer pointers. It means that this array can hold the address of 5 integer variables, or in other words, you can assign 5 pointer variables of type pointer to int to the elements of this array. arrop[i] gives the address of i th element of the array. So arrop[0] returns address of variable at position 0, arrop[1] returns address of variable at position 1 and so on.To get the value at address use indirection operator (*).So *arrop[0] gives value at address[0], Similarly *arrop[1] gives the value at address arrop[1] and so on.

Program:

#include <stdio.h>

#include <conio.h>

void swap( int *x, int *y )

{

    int t ;

    t = *x ;

    *x = *y ;

    *y = t ;

    printf(“In function :”);

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

}

void main( )

{

    int a,b;

    printf(“Enter the value of a : ”);

    scanf(“%d”, &a);

    printf(“Enter the value of b : ”);

    scanf(“%d”, &b);

    printf(“Before swapping : \n”);

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

    swap ( &a, &b ) ;

    printf(“After swapping : \n”);

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

    getch();

}

Output:

Enter the value of a : 10

Enter the value of b : 20

Before swapping :a=10  b=20

In function :

x=20 y=10

After swapping :

a=20 b=10