Is there a good reason for always enclosing a define in parentheses in C?

Question

Clearly, there are times where #define statements must have parentheses, like so:

#define WIDTH 80+20

int a = WIDTH * 2; // expect a==200 but a         


        

Answer 1

No. There is no case where #define WIDTH 100 can yield an unambiguous or "surprising" expansion. That's because it can only result in a single token being replaced by a single token.

As you know, macro confusion ensues when a single token (e.g. WIDTH) results in multiple tokens (e.g. 80 + 20). As far as I can surmise, that's the only cause for the use of parentheses in substitutions and, as explored in my first paragraph, it doesn't apply here.

However, this technical fact aside, it may still be a good practice. It promotes habit, and it also serves as a reminder if that macro ever gets modified to something more complex.