/**
 * buffon.c - Simulating Buffon's Needle Problem
 *
 * Authored by Jim Huang <jserv.tw@gmail.com>
 * Public Domain.  Runtime confirming to POSIX.1-2001.
 */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

int main( int argc, char **argv )
{
	int i;
	int ntrial = 99991; /* the largest prime number < 100000 */
	int crossing = 0;
	srand48( time( NULL ) );

	/*
	 * ----------------------------------------
	 * ||
	 * || 1                         
	 * ||                / ) Theta   ||x
	 * -----------------/----------------------
	 * x <= 1/2 * sin( Theta ), when needles cross a crack.
	 */
	for (i = 0; i < ntrial; i++) {
		double theta = M_PI * drand48(); /* 0 <= Theta <= PI */
		double x = drand48(); /* 0 <= x < 1 */
		if (x <= 0.5 * sin(theta))
			crossing++;
	}
	printf("Needles dropped on floor = %8d \n", ntrial);
	printf("Those that cross a crack = %8d \n", crossing);
	printf("\tPI Estimate: ");
	printf("%0.5f \n", (double)ntrial / (double)crossing);
	return 0;
}