array_change_key_case

Syntax:array array_change_key_case ( array $input [, int $case = CASE_LOWER ] )
Description: Changes all keys in an array

<?php
    $input_array = array("FirSt" => 1, "SecOnd" => 'Hai');
    print_r( array_change_key_case ( $input_array, CASE_UPPER ) );
?>

OUTPUT

<?php
Array ( 
[FIRST] => 1 
[SECOND] => Hai )
?>