Happy PI Day 2017

pi2017.c

/*
 * Happy PI Day '17
 */

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

const int COUNT = 1000000;
const int MAX = 1000000;

int gcd(int a, int b) {
    int temp;
    while (b != 0)
    {
        temp = a % b;

        a = b;
        b = temp;
    }
    return a;
}

int randint(int limit) {
    int divisor = RAND_MAX/(limit+1);
    int retval;

    do { 
        retval = rand() / divisor;
    } while (retval > limit);

    return retval + 1;
}

int main() {
    srand(time(NULL));
    int coprimes = 0;
    for (int i=0; i<COUNT; i++) {
        if (gcd(randint(MAX), randint(MAX)) == 1) {
            coprimes++;
        }
    }

    double x = ((double) coprimes) / COUNT;
    double pi = sqrt(6 / x);

    printf("%f\n", pi);

    return 0;
}