#include <iostream>
#include <future>
#include <chrono>
#include <vector>

using namespace std;

int sum(0);

int square(int x) {
  this_thread::sleep_for(chrono::milliseconds(100));
  cout << x << endl;
  cout << this_thread::get_id() << endl;
  return x * x;
}

int main() {

  vector<future<int>> av;
  future<int> a;

  for (int i = 1; i <= 20; i++) {
    av.push_back(async(launch::async, &square, i));
  }
  cout << this_thread::get_id() << endl;

  int v(0);
  for (auto& avs : av) {
    v = avs.get();
    sum += v;
  }

  cout << "The task returned " << sum << endl;
  return 0;
}