sleep - Sleep for the specified number of seconds
unsigned int sleep(unsigned int seconds);
sleep() makes the current process sleep until seconds seconds have
elapsed or a signal arrives which is not ignored.
Zero if the requested time has elapsed, or the number of seconds left to sleep.
sleep() may be implemented using SIGALRM; mixing calls to
alarm() and sleep() is a bad idea.
Using longjmp() from a signal handler or modifying the
handling of SIGALRM while sleeping will cause undefined results.