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
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 han-
dling of SIGALRM while sleeping will cause undefined