How to use #define to make a replacement in the header?

Question

C++ / C#

Let's say we have code:

//main.cpp
#define debug 1
#include "myHeader.h"
 . . .

and here is the contents of the header file:

// myHeader.h
#if debug == 1
 . . .
#else
 . . .
#endif

How to make everything work?

Answer 1

What compiler? Your code works for me (gcc)