How does this php code return odd numbers?

Question

Possible Duplicate:
Understanding PHP's & operator

I was just looking at array_filter() function doc and they had the following code to return odd numbers...

   <?php
    function odd($var)
    {
        // returns whether the input integer is odd
        return($var & 1);
    }
    ?>

Why does $var & 1 return odd number? how does that work?

See http://stackoverflow.com/questions/600202/understanding-phps-operator — AHungerArtist, Dec 21 '11 at 18:57
Also [Reference - What does this symbol mean in PHP?](http://stackoverflow.com/questions/3737139/reference-what-does-this-symbol-mean-in-php) — Herbert, Dec 21 '11 at 19:33

score 6 · Accepted Answer · answered Dec 21 '11 at 18:56

6

& is bitwise and. It acts as a mask on the bits of $var. All odd numbers end with 1

no  bit  &1
1   001  1
2   010  0
3   011  1
4   100  0
5   101  1
6   110  0
7   111  1

answered Dec 21 '11 at 18:56

knittl

Wow! Never even realized all the even numbers end with a 0 in binary. – CodeCrack Dec 21 '11 at 19:11

score 3 · Answer 2 · answered Dec 21 '11 at 18:59

You are using a bitwise function with always returns 1 when anded with an odd number.

A few examples:

 11 = 3
 01 = 1
----
 01 = odd -- return 1 (true)

 100 = 4
  01 = 1
-----
 000 = even -- return 0 (false)

One more:

 10101 = 21
    01 = 1
-------
 00001 = odd -- return 1 (true)

score 0 · Answer 3 · answered Dec 21 '11 at 19:00

That function return 1 if var is an odd number, 0 otherwise. "&" is the AND binary operator, so it considers the last binary digit of a number.

For example:

5 in binary is 101 -> 101 & 1 = 1 -> odd number.

8 in binary is 1000 -> 1000 & 1 = 0 -> even number.

3 Answers3