What is the proper #include for the function 'sleep()'?

Question

I am using the Big Nerd Ranch book Objective-C Programming, and it starts out by having us write in C in the first few chapters. In one of my programs it has me create, I us

Answer 1

What is the proper #include for the function 'sleep()'?

sleep() isn't Standard C, but POSIX so it should be:

#include