Hi,
Michael, include files are good thing ...as long as you take all project in your hands. Just imagine that those files are produced with different programmers and so both need to have fresh copy of include file to make own object file(s). Otherwise it requires to sync the include files any time an programmer tries to create object files. When some people work at big project then include files should contain as few non-modificable information as possible. For example, here most our shared include files contain only F1 definition ((=
The public/extrn declaration are useful when some programmers do each own object files and then a chief links them together. You know, object file should be created from the source one without any additional files presented. It is good-way programmer style. A compiler just needs with source code which contains references to external variables but not to thier values/locations etc. It is the work of the linker to put correct values into result code when it looks over all object files and collect enough information to do.
So, I have nothing against include files but try to avoid them at "group-programming".

cu