Question

Define pointer and its use. Explain array of pointer with example. Write program to swap the values by using call by reference concept. 

Answer 1

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.

Source Code :
//Program to swap the values by using call by reference concept.
#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