piStart.cpp

URL: http://147.64.242.52/~bennett/class/cmsc4000/spring2026/notes/ch3/code/piStart.cpp
 
#include <iostream>

// fork and wait
#include <unistd.h>
#include <signal.h>
#include <wait.h>

// 
#include <cmath>

using namespace std;

long double Pi(int iterations);

int main(int argc, char * argv[]) {

    int procs{10};
    int iterations {1'000'000};

    if (argc > 1) {
       int tmp{stoi(argv[1])};
       if (tmp > 1 and tmp < 1000) {
          procs = tmp;
       }
    }
    if (argc > 2) {
       int tmp{stoi(argv[2])};
       if (tmp > 1) {
          iterations = tmp;
       }
    }


    for(int i = 0; i < procs; ++i) {
        if (fork() == 0) {
           srand(time(nullptr)*(i+1));
           cout << " process " << i << " got " <<    Pi(iterations) << endl;
           return 0;
        }
    }

    for(int i = 0; i < procs; ++i) {
       wait(nullptr);
    }
}

long double Pi(int iterations){
    long double  pi{0};

    long long count{0};
    long double  x, y;
    for(int i = 0 ; i < iterations; ++i) {
       x = rand() / static_cast<long double>(RAND_MAX);
       y = rand() / static_cast<long double>(RAND_MAX);
       if (x*x + y*y <= 1) {
          ++count;
       }
    }

    return static_cast<long double>(count) 
           / static_cast<long double>(iterations) * 4;
}