Used to avoid double declarations of a header file.
C
Name does not matter, just be consistent.
#ifndef SOME_UNIQUE_NAME_HERE
#define SOME_UNIQUE_NAME_HERE
// body
#endifC++
Put #pragma once at the start of each header file.
This is what #pragma once does:
#ifndef SOME_UNIQUE_NAME_HERE
#define SOME_UNIQUE_NAME_HERE
// your declarations (and certain types of definitions) here
#endif