PHP get every third item of list

There are many ways. Here is a "oneliner":

<li class="<?php $t=$key%3; echo ($t==0?"one":$t==1?"two":"three");>

If you get more than 3 items you might get more manageable code with a switch statement:

<?php

switch($key%4){
case(0): echo "one"; break;
case(1): echo "two"; break;
case(2): echo "three"; break;
case(3): echo "four"; break;
}

?>

If you got your counter in your loop simple use modulo and check if it's 0. Then you can add the specific class.

if ($i % 3 == 0) { }

$classes = ['one', 'two', 'three'];

for (..) {
    printf('<li class="%s">', $classes[$key % count($classes)]);
}

<?php
$classes = array('first','second','third');
for ($i = 1; $i < 100; $i++) {
    echo $i.' class: ' .current($classes);    
    if(!next($classes))
    {
        // reset if there is end of array
        reset($classes);
    }    
    echo '<br/>';
}

elastic solution, You can have 3,4,5... classes by modifing $classes array only. Also is fast, don`t need to divide large numbers, just iterate small array with class listed in correct odrder

If you want clean HTML, define a function like below,

It will apply default class to every element, even class to every second element and third class to every third element, you can extend it as you like,

function apply_class($i)
{
    $every = 'default';
    $every_second = 'even';
    $every_third = 'third';

    $return [] = 'default';
    if ( $i%2 == 0 ) { $return [] = $every_second; }
    if ( $i%3 == 0 ) { $return [] = $every_third; }

    return implode(' ', $return);
}

Use it like,

<li class="<?php echo apply_class($i)?>" > </li>

Will render HTML like,

$i

1   <li class="default"> </li>
2   <li class="default even"> </li>
3   <li class="default third"> </li>
4   <li class="default even"> </li>
5   <li class="default"> </li>
6   <li class="default even third"> </li>
7   <li class="default"> </li>
8   <li class="default even"> </li>
9   <li class="default third"> </li>
10  <li class="default even"> </li>