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

using namespace std;

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

double pi{4};
mutex pi_mutex;

void ThreadFunction (int id, int nThread){

     int i;
     double sum{0};
     float signTerm = 1;

     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 += signTerm *4.0/static_cast<double>(i);
        }
     }

     lock_guard <mutex> guard(pi_mutex);
     pi += sum;

     return ;
}


int main() {
    vector<thread> threads;

    for(int i = 0; i < THREAD_COUNT; ++i) {
        thread t(ThreadFunction, i+1, 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;
}