Oh, the reason I had actually gotten on to the forum to make a post here in the first place (completely forgot when I saw the cal.h/cal.c update):

I am going to start using C99 features, so from now on (until/unless GCC finally supports C99 enough for the gnu99 dialect of C to be the default in your version of GCC), rdmod will need "--std=gnu99" to compile - or whatever it takes for your compiler of choice to compile in a C99-compatible manner.

Specifically, the reason I am doing this is to enable the use of the restrict keyword (I could use a less portable compiler extension that does the same thing even in the default gnu89 dialect, but I don't like using compiler-specific things), which allows the compiler to make some optimizations in the compiled end result. But since I am enabling it, I am also considering switching to inline declarations of the counter variable 'i' inside all of the loops, instead of declaring it once in main. I'd have to figure out which one executes faster, if the current way is faster then I'll keep it. That's later though. I really need to focus on other things and stop allowing myself to come back to this.