title: Define constant variables in C++ header
body: <p>A program I am working on has many constants that apply throughout all classes. I want to make one header file "Constants.h", and be able to declare all the relevant constants. Then in my other classes, I can just include <code>#include "Constants.h</code>. </p>
  
  <p>I got it to work fine using <code>#ifndef</code> ... <code>#define ...</code> syntax. However, I would prefer to use the <code>const int...</code> form of constants. I'm not quite sure how to though. </p>