몬테카를로 알고리즘 질문입니다.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
 
double pi(double tolerance)
{
	double x, y, val, error;
	unsigned long sampled = 0, hit = 0, i;
 
	do 
	{
		/* don't check error every turn, make loop tight */
		for (i = 1000000; i; i--, sampled++) {
			x = rand() / (RAND_MAX + 1.0);
			y = rand() / (RAND_MAX + 1.0);
			if (x * x + y * y < 1) hit ++;
		}
 
		val = (double) hit / sampled;
		error = sqrt(val * (1 - val) / sampled) * 4;
		val *= 4;
 
		/* some feedback, or user gets bored */
 
 
		printf("Pi = %f +/- %5.3e at %ldM samples.\r",
			val, error, sampled/1000000);
 
	} while (!hit || error > tolerance);
              /* !hit is for completeness's sake; if no hit after 1M samples,
                 your rand() is BROKEN */
 
	return val;
}
 
int main()
{
	printf("Pi is %f\n", pi(3e-4)); /* set to 1e-4 for some fun */
	return 0;
}