Sleep for milliseconds

Note that there is no standard C API for milliseconds, so (on Unix) you will have to settle for usleep, which accepts microseconds:

#include <unistd.h>

unsigned int microseconds;
...
usleep(microseconds);

In C++11, you can do this with standard library facilities:

#include <chrono>
#include <thread>

std::this_thread::sleep_for(std::chrono::milliseconds(x));

Clear and readable, no more need to guess at what units the sleep() function takes.