#include <iostream>
#include <iostream>
#include <iomanip>
#include <thread>
#include <mutex>
#include <vector>
#include <atomic>

using namespace std;

const int THREAD_COUNT{10};
const int COUNT_LIMIT{200'000'000};
const int KILL_LOOP{1};

void ThreadFunction (int id, atomic<double> & pi, const int nThread){
//void ThreadFunction (int id, double & pi, const int nThread){

     int i;
     float signTerm = 1;
     double sum ; 

     for(int j =0; j < KILL_LOOP; ++j) {
        sum = 0;
        for(i = id * 2 + 1; i < COUNT_LIMIT; i += 2*nThread) {
            if (i%4 ==1) {
               signTerm = 1;
            } else {
               signTerm = -1;
            }

            
           sum = sum + signTerm *4.0/static_cast<double>(i);
           //pi += signTerm *4.0/static_cast<double>(i);
           //pi.fetch_add( signTerm *4.0/static_cast<double>(i));
        }
     }

     pi.fetch_add(sum);

     return ;
}


int main() {
    vector<thread> threads;
    atomic<double> pi{4};
    //double pi{4};

    for(int i = 0; i < THREAD_COUNT; ++i) {
        thread t(ThreadFunction, i+1, ref(pi), THREAD_COUNT); 
        threads.push_back(move(t));
    }
    for( int i = 0; i < THREAD_COUNT; ++i) {
       threads[i].join();
    }


    cout << setprecision(10);
    cout << "Pi is approximately " << pi << endl;

    return 0;
}