#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define SIZE 128*1024
int main()
{
    int i,n=0;
    long long int num[SIZE],N;

printf("enter your aray value:\n");
    while(scanf("%lld",&N)!=EOF)
          {
              num[n]=N;
            n++;
        }

    for(i=n-1;i>=0;i--){

      printf("%0.4lf\n",(double)sqrt(num[i]));
    }
    return 0;
}

https://ideone.com/yjdxtz
Because you are allocating a large chunk of memory on the call stack

ohhh...thanks for your great suggestion.