- var_dump: documentation ( source)
- array_search: documentation ( source)
<?php
$arr = array(
"ONE"=>1,
"TWO"=>2,
"THREE"=>3,
"FOUR"=>4,
"FIVE"=>5,
"SIX"=>6,
"SEVEN"=>7,
"EIGHT"=>8,
"NINE"=>9,
"ZERO"=>0,
"UNKNOWN" => 'unknown',
);
var_dump(array_search('unknown', $arr));