Newbie Crypto question: MOD?

Ok folks, I recently received "Applied Cryptography" as a gift, and just have one question: How does the MOD function work in crypto functions? It seems to work differently than what I've seen before, i.e.: C/C++ MOD. I also didn't see anything in TCM's FAQ... If this is considered noise, I apologize in advance. "Freedom is meaningless unless | ic58@jove.acs.unt.edu - James Childers you can give to those with whom| No man's freedom is safe you disagree." - Jefferson | while Congress is in session EA 73 53 12 4E 08 27 6C 21 64 28 51 92 0E 7C F7