Question

I have written the following C program. The output is 32. Why is this?

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#define max 10+2

int main(){
    int i;
    i = max * max;
    printf("\n%d\n",i);

    return 0;
}

(I am learning C and am relatively new to it.)

Answer 1

#define max 10+2

This is the preprocessor. it is not smart.

it is stupid.

it just replaces text.

max*max

will resolve to

10+2*10+2

which is

10+(2*10)+2

because of operator precedence, which is

10 + 20 + 2

i.e. 32

Furthermore, you should avoid preprocessor macros whenever you can and use static const instead. You may or may not want to also consider using a const variable or an enum instead of a #define; each have their tradeoffs, refer to the similar question: "static const" vs "#define" vs "enum".

If you want to stick to preprocessor, then you could just use:

#define max (10+2)

Since parenthesised code will take operator precendence.