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

Whenever the define consists of a single token (one operand only, no operators), the parentheses are not needed because a single token (such as 100) is an indivisible atom when lexing and parsing.