calloc() is used to allocate the memory, which will be equal to the value, "num*size". Function returns a pointer to the first byte of the allocated space.If there is no space to allocate, a "NULL" pointer is returned.

    void *calloc(size_t num, size_t);   

#include <stdlib.h>
#include <stdio.h>
int main()
  {
     unsigned num;
     int *ptr;
     printf("Enter the number to allocate: ");
     scanf("%d", &num);
     ptr = (int*)calloc(num, sizeof(int));
     if (ptr != NULL)
        puts("Memory allocation was successful.");
     return(0);
 }

   Enter the number to allocate: 1000
   Memory allocation was successful

In the above Dynamic allocation function example the number parameter for the "calloc()" is got as input. Once the memory is allocated a message is displayed.