Simple function to approximate the value of pi.

pi_calc.c

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

int main(void) {
    double x, y, i; // variables
    double N0 = 0, Ntot = 100000000; // numbers that the numbers in the range and total numbers
    double A; // area var


    srand(time(NULL)); // initialize the random seed

    for( i = 0; i < Ntot; i++){
	/**
	 Lets find how many random values will be within the radius
	 of 1, so that we could approximate the value of pi
	*/

        x = rand() / (double)RAND_MAX;
        y = rand() / (double)RAND_MAX;

        if ((x*x + y*y) < 1) N0++;
    }
    // Area is approximately number in the range over total numbers
    A = (double)N0/(double)Ntot;

    // Since we checked only the area of the quarter of the circle,
    // we need to find the full circle by multiplying by four
    printf("Pi is %.30f\n", 4*A);
    return 0;
}