#include <algorithm>
#include <future>
#include <numeric>
#include <thread>

bool is_prime(int n)
{
    if (n <= 1) return false;
    if (n == 2) return true;
    for (int i { 3 }; i * i <= n; ++i)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}

void task(std::vector<int>& v, std::promise<int> promise)
{
    int count { std::count_if(v.begin(), v.end(), is_prime) };
    promise.set_value(count);
}

int main()
{
    std::vector<int> v(1000);
    std::iota(v.begin(), v.end(), 1);

    std::promise<int> promise { };
    auto future = promise.get_future();

    std::jthread thread { task, std::ref(v), std::move(promise) };

    std::cout << "The number of primes is: ";
    std::cout << future.get() << std::endl;
}