#include <stdio.h>
#include <stdlib.h>

#define N 1000

double f(double x, double y) { return 1.0 - (x * x) - (y * y); }

int main()
{
  int i, j;
  double sum, z;

  sum = 0.0;
  for (i = -N; i < N; i++) {
    for (j = -N; j < N; j++) {
      if ((z = f((double)i / N, (double)j / N)) > 0.0) {
        sum += z * (1.0 / N) * (1.0 / N);
      }
    }
  }
  printf("%lf\n", sum);
}
/* end */

1.570796

Exited: ExitFailure 9