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When defining macros, put parentheses around all variable names.   This ensures that the macro is evaluated in a predictable manner.

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#define PRODUCT(A,B) A * B
int a = PRODUCT(3+4, 5)

PRODUCT(3+4, 5) is converted to 3+4 * 5 by the preprocessor, which the compiler will then intrepret intreprets as 3+(4*5) = 23. This Presumably, this does not match what the intended behavior of the macro name implies the behavior to be, which is (3+4) * 5 = 35.

Compliant Code Example

#define PRODUCT(A,B) (A) * (B)
int a = PRODUCT(3+4, 5)

Due to the parenthesesBy adding parentheses around each argument, this macro is evaluated (correctly) evaluates to 35, matching what the macro name implies it should.