How does the following program work?

Question

#include<stdio.h>
#define SQR(x) (x*x)
int main(){
int a;
a= SQR(3-4);
printf("%d",a);
return 0;
}

Output :-13

How does the macro function work here to give the output as -13?

It works as follows: `3-4*3-4`.To get correct answer,use `#define SQR(x) ((x)*(x))` — 0xF1, May 27 '14 at 12:18
@Mauren: What's the difference? `+` and `-` have same precedence. — 0xF1, May 27 '14 at 12:20
@Rohan surely they do, I was just wondering the order in which the calculations take place. — Mauren, May 27 '14 at 12:21

score 1 · Answer 1 · answered May 27 '14 at 12:18

The expression inside SQR gets 3-4*3-4, and given the precendence of operators, gives you that result. This is a common mistake in macros. In principle, every argument should be surrounded with parentheses, if it involves some calculation:

#define SQR(x) ((x)*(x))

You'll get the expected result.

How does the following program work?

1 Answers1