# How to check if a number is odd or even with PHP?

In mathematics, one of the definitions of odd and even number is that they can be expressed like this (where n is the number and k is an integer):

Odd numbers: n = 2k +1

Even numbers: n = 2k

In PHP, we can check a number’s parity by checking the remainider of the division of this number by 2 using the modulus operator (%), if the remainder is 1, the number is odd, if the remainder is 0, the number is even, let’s write some functions for this:

```<?php
function is_odd(\$n){
return (boolean) (\$n % 2);
}

function is_even(\$n){
if(is_odd(\$n))
return FALSE;
return TRUE;
}

\$a = 1;
\$b = 2;
\$c = 3;

echo "\$a is ",  is_odd(\$a) ? 'odd' : 'even' , '.<br />';
echo "\$b is ",  is_odd(\$b) ? 'odd' : 'even' , '.<br />';
echo "\$c is ",  is_even(\$c)? 'even' : 'odd' , '.<br />';

?>```

The output in the browser will look like:

1 is odd.
2 is even.
3 is odd.

This is a simple way to do it, I used typecasting in the function is_odd() so it’s always return TRUE or FALSE, instead of 1 or 0.

#### PHP modulus (%)

Operands of modulus are converted to integers (by stripping the decimal part) before processing.

```<?php
echo    1 % 2;
echo 1.01 % 2;   // each of these three statements outputs 1.
echo 1.99 % 2;
?>```