title: What is the proper #include for the function 'sleep()'?
body: <p>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 use the sleep function. In the book it told me to put <code>#include &lt;stdlib.h&gt;</code> under the <code>#include &lt;stdio.h&gt;</code> part. This is supposed to get rid of the warning that says "Implicit declaration of function 'sleep' is invalid in C99". But for some reason after I put <code>#include &lt;stdlib.h&gt;</code>, the warning does not go away.. This problem does not stop the program from running fine, but I was just curious on which <code>#include</code> I needed to use!</p>