#include <cmath>

#include <future>

#include <iostream>

#include <numeric>

#include <stdexcept>

#include <thread>

void throw_exception() {

throw std::invalid_argument("input cannot be negative");

}

void calculate_squre_root(std::promise<int> &prom) {

int x = 1;

std::cout << "Please, enter an integer value: ";

try {

std::cin >> x;

if (x < 0) {

throw_exception();

}

prom.set_value(std::sqrt(x));

} catch (std::exception &) {

// Propagate exception!

prom.set_exception(std::current_exception());

}

}

void print_result(std::future<int> &fut) {

try {

int x = fut.get();

std::cout << "value: " << x << '\n';

} catch (std::exception &e) {

std::cout << "[exception caught: " << e.what() << "]\n";

}

}

int main() {

std::promise<int> prom;

std::future<int> fut = prom.get_future();

std::thread printing_thread(print_result, std::ref(fut));

std::thread calculation_thread(calculate_squre_root, std::ref(prom));

printing_thread.join();

calculation_thread.join();

}