#include <iostream>
#include <string>
#include <thread>
#include <vector>

// Here we have a race condition on variable value.

int main(int argc, char *argv[]) {
  if (argc != 2) {
    std::cerr << "Please give the desired number of threads"
                 " in the command line.\n";
    return 1;
  }

  int value;

  int const n_threads = std::stoi(argv[1]);
  if (n_threads <= 0) {
    std::cerr << "Number of threads must be positive.\n";
    return 2;
  }

  std::vector<std::thread> threads;

  for (int i = 0; i < n_threads; ++i) {
    threads.emplace_back([&value](int id) { value = 2 * id; }, i);
  }

  for (auto &thd : threads) {
    thd.join();
  }

  // Guess what will be printed.
  std::cout << "Value is " << value << std::endl;
}