#define MUX(a,b) a*b
MUX(10-5,10+5) = 10+5*10-5 = 10+50-5 = 55
I think MUX(10-5,10+5) = (10-5)*(10+5) = 75, but it's wrong.
Why? Can anyone explain?
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1That's why you should yse parens around macro arguments – stark May 27 '21 at 11:18
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2Replace `#define MUX(a,b) a*b` with `#define MUX(a,b) ((a)*(b))` and you will get the desired behavior. – Andreas Wenzel May 27 '21 at 11:19
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1If you study the output of the preprocessor you'll understand why. See the link of the duplicate. – klutt May 27 '21 at 11:19
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duplicate: [The need for parentheses in macros in C](https://stackoverflow.com/q/10820340/995714), – phuclv May 27 '21 at 11:32
1 Answers
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It's because macro replacement is entirely textual. If you want parentheses for correct arithmetic, they must be in the replacement text.
Jens
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Macro replacement is based on preprocessor tokens; it is not entirely textual. – Eric Postpischil May 27 '21 at 12:18