[GCC] error : Sleep was not declared in this scope

Situation:
I got error message when I compiling my c++ code with sleep(1); inline.
"error : Sleep was not declared in this scope"


Solution:
The solution is add folling including message in the head of your code.
#include <unistd.h>


Reference:
http://stackoverflow.com/questions/10976176/c-error-sleep-was-not-declared-in-this-scope