Understand the Use of realloc() Function

/*
Write a program to understand the use of realloc() function
*/

#include<stdio.h>
#include<stdlib.h>
main( )
{
    int i, *ptr;
    ptr = (int *)malloc(5 *sizeof(int));
    if(ptr == NULL)
    {
        printf("Memory not available\n");
        exit(1);
    }
    printf("Enter 5 integers : ");
    for(i=0; i<5; i++)
        scanf("%d", ptr+i);
    /*Allocate memory for 4 more integers*/
    ptr = (int *)realloc(ptr, 9*sizeof(int));
    if(ptr == NULL)
    {
        printf("Memory not available\n");
        exit(1);
    }
    printf("Enter 4 more integers : ");
    for(i=5; i<9; i++)
        scanf("%d", ptr+i);
    for(i=0; i<9; i++)
        printf("%d ", *(ptr+i));
}