[C++] Number of CPU threads

#include <iostream>
#include <thread>


// main function
// entry point to the application
int main() {

#ifdef __APPLE__
    std::cout << "This is a Mac running a darwin based system" << std::endl;
#endif

#ifdef __WIN32__
    std::cout << "This is a PC running a 32 or 64-bit version of Windows" << std::endl;
#endif

#ifdef __WIN64__
    std::cout << "This is a PC running a 64-bit version of Windows" << std::endl;
#endif

#ifdef __linux__
    std::cout << "This is a PC running Linux" << std::endl;
#endif


    // a standard function to get the number of available threads
    unsigned int n = std::thread::hardware_concurrency();

    // printing out the number of threads to the standard output
    std::cout << n << " concurrent threads are supported.\n";

    // normal run returns zero
    return 0;
}