main.c


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/*
 * Celebrate Pi day in C.
 *
 * See https://www.youtube.com/watch?v=RZBhSi_PwHU to watch Matt Parker
 * do it the hard way.
 *
 * See https://www.youtube.com/watch?v=LFwSIdLSosI for a more in-depth
 * explanation of why this works.
 */

#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define NR_PAIRS 1000000

static unsigned int
gcd(unsigned int a, unsigned int b)
{
    unsigned int tmp;

    while (b != 0) {
        tmp = b;
        b = a % b;
        a = tmp;
    }

    return a;
}

static bool
coprimes(unsigned int a, unsigned int b)
{
    return (gcd(a, b) == 1);
}

int
main(int argc, char **argv)
{
    unsigned int i, total;
    double pi;

    srand(time(NULL));

    for (i = 0, total = 0; i < NR_PAIRS; i++) {
        if (coprimes(rand(), rand())) {
            total++;
        }
    }

    /* Division by zero ? What's the problem ? */
    pi = sqrt(6. * NR_PAIRS / total);
    printf("%f\n", pi);
}