Hi.

I've included <math.h> and have tried to use sqrt(). Why I wasn't
allowed to do this and have got CE?

Source code follows:

#include <stdio.h>
#include <math.h>
int getint() { int i; scanf("%d", &i); return i; }

int main()
{
  int i = getint();
  while(i--)
  {
    int n = getint() - 1;
    int nn = sqrt(n+n);

    if(nn*(nn+1) == n+n)
      printf("1\n");
    else
      printf("0\n");
  }
}