Anything involving the preprocessor ranks high in my favorite C trick (I once got a "clever abuse of the C preprocessor" notation after writing a C+ library for

Anything involving the preprocessor ranks high in my favorite C trick (I once got a "clever abuse of the C preprocessor" notation after writing a C+ library for school written entirely using macros). Actually, anything involving meta-programming is "cool". Knowing a language is "easy" once you get the logic, but manipulating the language to do the work for you is even more satisfying.