My learning of concurrent programming in C++11

hw.cpp

#include <iostream>
#include <thread>

void hello()
{
    std::cout << "HW!" << std::endl;
}

int main()
{
    std::thread t(hello);
    t.join();
}

threadsInBackground.cpp

/* One thread prints an incrementing counter each second,
 * while the second thread is waiting for user to enter
 * anything to terminate the program */

#include <unistd.h>
#include <string>
#include <chrono>
#include <thread>
#include <iostream>

class Counter {
    private:
        int counter;
    public:
        Counter() : counter(0) { }
        void operator() () {
            std::cout << counter++ << std::endl;
            std::this_thread::sleep_for(std::chrono::milliseconds(1000));
        }
};

int main()
{
    Counter counter;
    std::thread counterThread(counter);
    counterThread.detach();

    std::string userInput;
    while (std::cin >> userInput)
        ;
}