OK thanks for the additional info. I will definitely experiment with both of these techniques.

Good, this is very useful information. I think I will go with the repository option. It's largely a matter of taste, but being a C programmer, I finally swore off the preprocessor. The point to emphasize, if I am understanding correctly, it that these are two separate approaches. Somehow I had it in the back of mind that to split files, I would need something resembling a combination of both of these approaches at the same time.