Getting to Know The Modulus Operator (%) in PHP

I ran across this code in the index.php file of Alexander Agnarson’s fantastic free Wordpress theme Hueman
and couldn’t figure out what it did:

<?php if($i % 2 == 0) { echo '</div><div class="post-row">'; } $i++; endwhile; echo '</div>'; ?>

Specifically,  the part with the % sign:

($i % 2 == 0)

After some searching, I discovered that the percent sign was also known as the modulus operator, which works like this:

<?php

$a % $b  // Displays the REMAINDER after $a is divided by $b

// Examples
6 % 2 = 0  // 6 is divided by 2 three times with 0 remaining
5 % 2 = 1  // 5 is divided by 2 two times with 1 remaining
4 % 2 = 0  // etc..
3 % 2 = 1
2 % 2 = 0
1 % 2 = 1
0 % 2 = 0

?>

In the theme, this code helps form the 2-across grid layout displaying blog posts on the homepage:

<?php 
	if($i % 2 == 0) { 
		echo '</div><div class="post-row">'; 
	} 
	$i++; 
	endwhile; 
	echo '</div>'; 
?>

In other words, $i serves as the number of blog posts cycling through the query loop. Everytime that number of posts equals a group of 2 (resulting in nothing left over, i.e. == 0), the code wraps the pair in closing and opening div tags.

Pretty neat!

Other resources:

Khan Acadmeny – What is Modular Arithmetic?