array_php() function in php

Question

for array_filter, I considered an example from php official site. I found a example there

function odd($var)
{
 // returns whether the input integer is odd
 return($var & 1);
}
function even($var)
{
 // returns whether the input integer is even
 return(!($var & 1));
}

both function return return($var & 1) and return(!($var & 1)); I can not understand properly what does it mean and specially why 1 is there in return

• fedorqui: possible duplicate of Understanding PHP & (ampersand, bitwise and) operator
• Masiorama: Actually the returns are different. I suggest what @fedorqui commented just right before me.
• Forien: I would suggest reading this topic: stackoverflow.com/questions/3737139/…

Answer 1

It's pretty simple: & is a bitwise AND operator and it works as followed:

 A | B
---------------
 0 | 0 -> 0
 1 | 0 -> 0
 0 | 1 -> 0
 1 | 1 -> 1

And if you take as an example 2, 3 and 6 for odd then this is what's going on:

0000 0010 -> 2
0000 0001 -> 1
--------- &
0000 0000 = return 0

0000 0011 -> 3
0000 0001 -> 1
--------- &
0000 0001 = return 1

0000 0110 -> 6
0000 0001 -> 1
--------- &
0000 0000 = return 0

So in other words if the first digit (1) is 'on' it's going to return 1 because it's odd and if not it's going to return 0

And the same is going on for even just with a NOT (!) operator