What are C macros useful for?

Question

I have written a little bit of C, and I can read it well enough to get a general idea of what it is doing, but every time I have encountered a macro it has thrown me complet

Answer 1

One of the obvious reasons is that by using a macro, the code will be expanded at compile time, and you get a pseudo function-call without the call overhead.

Otherwise, you can also use it for symbolic constants, so that you don't have to edit the same value in several places to change one small thing.