mote_carlo.c

/* this porgram solves PI by mote carlo method. */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX_NUM 100000

double monte_carlo();

int main()
{
    printf("%lf\n", monte_carlo());
    return 0;
}

in_circle(double x, double y)
{
    int ret = 0;
    if(0.5 > sqrt(x * x + y * y)) {
        ret = 1;
    }
    else {
        ret = 0;
    }
    return ret;
}

double monte_carlo()
{
    int i,
        count_in_circle = 0,
        count_in_square = 0;
    double x, y,
           ret_pi;
    srand(time(NULL));

    for(i = 0; i < MAX_NUM; i++) {
        x = ((double)rand() / (double)RAND_MAX) - 0.5;
        y = ((double)rand() / (double)RAND_MAX) - 0.5;
        if(in_circle(x,y)) {
            count_in_circle++;
        }
        count_in_square++;
    }
    ret_pi = (double)count_in_circle / MAX_NUM * 4;
    return ret_pi;
}