/*
 * Program to estimate pi using "Monte Carlo" method:
 * 
 * Simulates throwing darts at a dartboard with a quarter circle and
 * counting how many are inside the (quarter) circle.
 */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/* best(?) available value of pi, to check computed approximation */
/* surprisingly, no library-defined constant for this in standard C! */
#define M_PI acos(-1.0)

int main(void) {

	long samples;
	int seed;
	printf("samples, seed?\n");
	if (scanf("%ld %d", &samples, &seed) != 2) { 
		printf("values not integers\n");
		return 1;
	}
	srand(seed);

	long in_circle = 0;

	/* simulate throwing darts at a dartboard with a quarter-circle */
	for (int i = 0; i < samples; ++i) {
		double x = (double) rand() / (double) RAND_MAX;
		double y = (double) rand() / (double) RAND_MAX;
		if ((x*x + y*y) < 1.0) {
			in_circle += 1;
		}
	}

	double est_pi = 4 * (double) in_circle / samples;

	printf("result for %ld samples and seed %d:\n%22.20f (differs from M_PI by %g)\n", 
			samples, seed, est_pi, est_pi - M_PI);
	return 0;
}