Objective C - Why do constants start with k

Why do constants in all examples I've seen always start with k? And should I #define constants in header or .m file?

I'm new to Objective C, and I don't know C. Is there some tutorial somewhere that explains these sorts of things without assuming knowledge of C?

Starting constants with a "k" is a legacy of the pre-Mac OS X days. In fact, I think the practice might even come from way back in the day, when the Mac OS was written mostly in Pascal, and the predominant development language was Pascal. In C, #define'd constants are typically written in ALL CAPS, rather than prefixing with a "k".

As for where to #define constants: #define them where you're going to use them. If you expect people who #import your code to use the constants, put them in the header file; if the constants are only going to be used internally, put them in the .m file.

Current recommendations from Apple for naming constants don't include the 'k' prefix, but many organizations adopted that convention and still use it, so you still see it quite a lot.