Multi line preprocessor macros

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You use \ as a line continuation escape character.

#define swap(a, b) {               \
                       (a) ^= (b); \
                       (b) ^= (a); \
                       (a) ^= (b); \
                   }

EDIT: As @abelenky pointed out in the comments, the \ character must be the last character on the line. If it is not (even if it is just white space afterward) you will get confusing error messages on each line after it.

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