#include <stdio.h>
#include <math.h>
void main()
{
  __int64 d;
  printf("Enter EOF for end\n");
  while(scanf("%I64d",&d)!=EOF)
   if(d<=(10<<8)*100)printf("%.4f\n",sqrt(d));
}

Because int main(void){
return 0;
}

It is not the main problem (though also the problem). Major troublemaker is the line:

printf("Enter EOF for end\n");

Why do you do this? The problem statement doesn'n tell you to output "Enter EOF for end"...