<?php$ar1 =array ("first" => "первый","second" => "второй");$ar2 = array ( "первый", "второй");print_r($ar1);print_r($ar2);?>
( [first] => первый [second] => второй)Array( [0] => первый [1] => второй)
print_r(array_keys($ar1,"первый"));Array( [0] => first)