Do you #define booleans?

Do you? What's wrong with simple one and zero?

What are the rules for preprocessor processing?

What happens if you do:

#define true false
#define false true
printf("%d\n", false);

What about

#define "one" "two"
#define "two" "three"
#define "three" "one"
printf("%s %s %s\n", "one", "two", "three");

Sorry, don't have a C compiler at hand to test. I do know some defines might apply one after another, but not the fine rules of them.