time_measure

#include <thread>
#include <chrono>
#include <random>
#include <vector>
#include <iostream>
#include <numeric>

int BIG = 10000;
std::vector<double> for_sum;
std::vector<double> array;

void job(int num, int numberOfThreads) {
    size_t start = num * (BIG / numberOfThreads), finish;
    if (num + 1 < numberOfThreads) {
        finish = (num + 1) * (BIG / numberOfThreads);
    }
    else {
        finish = BIG;
    }
    for_sum.push_back(std::accumulate(array.begin() + start, array.begin() + finish, 0));
}

int main() {
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_real_distribution<> dis(0, 10000);
    int numberOfThreads = 1;
    for (;numberOfThreads < 20; numberOfThreads++) {
        std::vector<std::thread> threads;
        for (int i = 0; i < BIG; i++) {
            array.push_back(dis(gen));
        }
        double ans = 0;
        std::chrono::steady_clock::time_point start, end;
        start = std::chrono::steady_clock::now();
        for (int i = 0; i < numberOfThreads; i++) {
            threads.push_back(std::thread(job, i, numberOfThreads));
        }
        ans = std::accumulate(for_sum.begin(), for_sum.end(), 0);
        end = std::chrono::steady_clock::now();
        for (auto&& t : threads)
            t.join();
        std::cout << numberOfThreads << ' ' << (end - start).count() << std::endl;
    }
    return 0;
}