<?php
$c = array();
// You store some data using some string keys
foreach (array('ab', 'cd', '10', 'gh', '24') as $key) {
$c["$key"] = 1;
}
// You pass the array $c to some place else and there you do something like
foreach ($c as $k => $v) {
if ($k === "10") {
echo "found";
exit;
}
}