How to check if a variable is even in C

Question

How can I check if a variable (an int) is even (that is, not odd) in C without using "%" operator? I am running on linux platform.

Thank you.

I don't think the platform has anything to do with the question. @abelenky The question makes total sense for me. — m0skit0, Mar 14 '14 at 19:48
@abelenky How to check if a number is even without using modulus? I don't see where's the problem — m0skit0, Mar 14 '14 at 19:49
@abelenky: Instead of doing number % 2, he wants another way. — Engineer2021, Mar 14 '14 at 19:49
I was confused by the usage of "even". eg: ***"Is that even a defined variable?"***, vs. ***"Is that numeric value divisible by 2?"*** — abelenky, Mar 14 '14 at 19:50

score 9 · Accepted Answer · answered Mar 14 '14 at 19:48

9

if (!(v & 1))

should be true for even numbers

answered Mar 14 '14 at 19:48

Jason Goemaat

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I google it and see people using 'return (((a>>1)<<1) == a)'. Why this solution is suggested, what case does it cover that (V&1) does not? – michael Mar 14 '14 at 23:00
might be different for negative numbers on systems with certain representations of negative integers? – Jason Goemaat Mar 15 '14 at 17:52

score 3 · Answer 2 · answered Mar 14 '14 at 19:49

3

Try bitwise AND with 0x01 to check if last binary digit is 0 or 1.

In case of 0 it's even, whereas in case of 1 it's odd.

answered Mar 14 '14 at 19:49

chrk

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*"0x01"* Why not 0x0001? 1 is enough :) – m0skit0 Mar 14 '14 at 19:50

score 0 · Answer 3 · answered Mar 14 '14 at 20:21

0

Just for providing an alternative answer, not that this is any better... You could use the following comparison to check whether an int is even (divisible by 2), where asd shall be an int:

asd == asd / 2 * 2;     //returns 1 (true) if asd is even

answered Mar 14 '14 at 20:21

Utkan Gezer

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How to check if a variable is even in C

3 Answers3