I got the book (second printing) on Friday.
on page 32 of chapter 5, one is supposed to #include to get rid of the warning about the implicit use of sleep().
Doing so did not eliminate the error.
I poked around and found sleep() in . When I #included this file, the warning went away. The search of the documentation did not show sleep() in any other library.
This may be related -- on p28, the warning about the lack of a function prototype did not appear.
Xcode version 4.3.2 (4E2002), and OS X 10.7.3