"Monte Carlo" example (Introductory C++)

main.cc

/*
phdp@dell-xps:~$ vim main.cc 
phdp@dell-xps:~$ clang++ -std=c++11 main.cc -o main
phdp@dell-xps:~$ time ./main
The seed is 1375464851
3.14157

real	0m27.375s
user	0m27.308s
sys	0m0.004s
phdp@dell-xps:~$ clang++ -O3 -std=c++11 main.cc -o main
phdp@dell-xps:~$ time ./main
The seed is 1375464890
3.14165

real	0m1.769s
user	0m1.764s
sys	0m0.000s
*/

#include <iostream>
#include <random>
#include <ctime>

using namespace std;

int main() {
    const unsigned int seed = time(0);
    cout << "The seed is " << seed << endl;

    mt19937_64 rng(seed);
    uniform_real_distribution<double> unif;

    const unsigned int iterations = 100000000;
    unsigned int inside = 0;

    for (int i = 0; i < iterations; i++) {
        const double x = unif(rng);
        const double y = unif(rng);
        if (x * x + y * y < 1.0) {
            inside++;
        }
    }

    cout << 4.0 * ((double)inside / iterations) << endl;

    return 0;
}