There is absolutely no way that a properly maintainable piece of code, be it coded by one or by a group, can be made without a common set of definitions. So, if you do not have a .h/.inc file that defines everything used by more than one module you will have a maintenance nightmare. If you buy a piece of software in object form only it comes with a .h file that you must include in your own .h file. That file typically will include something like

#ifdef master
char Ralph;
#else
extern char Ralph;
#endif

and then one and only one of your modules define master.

Erik