darts.c

用概率算法计算pi的值

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

#define frand() ((double) rand() / (RAND_MAX + 1.0))

/*** A random algorithm for Pi's value.***/
int main(int argc, char *argv[])
{
	long i, k = 0, n;
	double x, y, pi;

	if(argc != 2) {
		printf("usage: %s n\nNote: n is unsigned integer\n", argv[0]);
		exit(0);
	}
	n = atol(argv[1]);
	printf(" n's value: %ld \n", n);
	printf(" RAND_MAX's value: %d \n", RAND_MAX);

	srand( (unsigned)time( NULL ) );
	for(i = 0; i < n; i++)
	{
		x = frand();
		y = frand();
		if(x*x + y*y <= 1) k++;
	}
	printf(" k's value: %ld \n", k);
	pi = 4.0L * k / n;
	printf("Pi: %lf\n", pi);
	return 0;
}