why is this behaviour with MACRO? [closed]

Question

I've the following code.if i give control_word as 6 why if condition evaluates to true and enters inside if block?what exactly is happening here?

#define MACRO1 0x01
#define MACRO2 0x02
#define MACRO4 0x04
#define MACRO3 MACRO1 | MACRO2
#define MACRO7 MACRO4 | MACRO3

int main()
{
    if(control_word == MACRO3 || control_word == MACRO7)
    {
        /*DO SOME OPERATION*/
    }
    else
    {
        /*DO SOMETHING ELSE */
    }

}

Answer 1

The precedence of the | and == operators is not that you think it is. Moral: always parenthesize your macros!

#define MACRO3 (MACRO1 | MACRO2)
#define MACRO7 (MACRO4 | MACRO3)

So what happens is the expression expands to

control_word == 0x01 | 0x02 || control_word == 0x01 | 0x02  | 0x04

which in turn forms

(control_word == 1) | 2 || (control_word == 7) | 6)

that is

0 | 2 || 0 | 6

so all in all it's

2 || 6

which is interpreted by C as "true or true", and that yields true.