realloc() Function in C

Program 1

//Program for realloc function
#include<stdio.h>
#include<conio.h>
#include <stdlib.h>
#define clrscr() system("cls")
int main()
{
        int *ptr=NULL;
        ptr=(int *)malloc(2*sizeof(int));
       // clrscr();
        if(ptr==NULL)
        {
            printf("Memory not allocated");
            //exit(0);
        }
        else
        {
            printf("Enter two Number");
            for(int i=0;i<2;i++)
            {
                scanf("%d",ptr+i);
            }
            ptr=(int*)realloc(ptr,4*sizeof(int));
            if(ptr==NULL)
           {
            printf("Memory not allocated");
            //exit(0);
           }
          else
          {
            printf("Enter next two Number");
            for(int i=2;i<4;i++)
            {
                scanf("%d",ptr+i);
            }
            int sum=0;
            printf("Elements are: ");
            for(int i=0;i<4;i++)
            {
              printf("%d\n",*(ptr+i));
               sum=sum+*(ptr+i);
            } 
            printf("Sum is %d",sum);
            free(ptr);
         }   
        }
}