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

When code defines only a number, @Alexander Gessler well answers the question.

Yet many coders do not notice the unary operators in the following:

#define TEMPERATURE1M (-1)
#define TEMPERATURE1P (+1)

When code uses a #define that employs an operator, enclosing () insures expected numeric results and precedence.

#define TEMPERATURE_WITH  (-1)
#define TEMPERATURE_WITHOUT -1

// Consider how these will compile
int w  = 10-TEMPERATURE_WITH;
int wo = 10-TEMPERATURE_WITHOUT;  // May not compile

The last line of code may compile given C99 semantic changes @Olaf