Programming iOS 6, 3rd Edition

Compilation, Statements, and Comments

C is a compiled language. You write your program as text; to run the program, things proceed in two stages. First your text is compiled into machine instructions; then those machine instructions are executed. Thus, as with any compiled language, you can make two kinds of mistake:

• Any purely syntactic errors (meaning that you spoke the C language incorrectly) will be caught by the compiler, and the program won’t even begin to run.
• If your program gets past the compiler, then it will run, but there is no guarantee that you haven’t made some other sort of mistake, which can be detected only by noticing that the program doesn’t behave as intended.

The C compiler is fussy, but you should accept its interference with good grace. The compiler is your friend: learn to love it. It may emit what looks like an irrelevant or incomprehensible error message, but when it does, the fact is that you’ve done something wrong and the compiler has helpfully caught it for you. Also, the compiler can warn you if something seems like a possible mistake, even though it isn’t strictly illegal; these warnings, which differ from outright errors, are also helpful and should not be ignored.

I have said that running a program requires a preceding stage: compilation. But in fact there is a third stage that precedes compilation: preprocessing. (It doesn’t really matter whether you think of preprocessing as a stage preceding compilation or as the first stage of compilation.) ...