bit operation problem

I got a interview question previous like this:
find what might be wrong

if (mask & ASYNC_BIT == 0x0100) {....

No values were defined for both "mask" and ASYNC_BIT in the question, just wonder in what condition the result of "AND" operation could not compare with hex value.

:p

Syntactically: == comes first, & comes second.

The order of precedence between those operations are "bad": you first do the ==, then do the and for some reason. You need parenthesis to make it right, e.g.

Code:

---

if ((mask & ASYNC_BIT) == 0x0100)

---

Without parenthesis, it becomes:

Code:

---

if (mask & (ASYNC_BIT == 0x0100))

---

which turns into an and with either 1 or 0.

--
Mats

Oh that's really basic thing and I understand why i made a mistake then.
thx

I wouldn't have known that without looking at a precedence table. I'd tell the interviewers I can answer the question if they either show me a precedence chart or put some parentheses in. :p

Quote:

---

Originally Posted by pinklax

Oh that's really basic thing and I understand why i made a mistake then.
thx

---

Aside from cpjust's answer, I have made the mistake of writing code like that so many times that I'm now ACTIVELY thinking about it when I'm writing bit-checking/bit-twiddling code - a bit like someone who's flooded the bathroom 6 times will double and tripple-checkl that they haven't left the taps on.

--
Mats