title: Using the same variable across multiple files in C++
body: <p>In the process of changing some code, I have spilt some functions into multiple files. I have the files <code>controls.cpp</code> and <code>display.cpp</code> and I would like to be able to have access to the same set of variables in both files. I don't mind where they are initialized or declared, as long as the functions in both files can use them.</p>
  
  <p>This was not an issue when the functions were in the same file, but now it seems almost impossible after an hour of googling and trying various things.</p>