$letters = array(
"a"=>"A",
"b"=>"B",
//...
"z"=>"Z"
);
function mystrtoupper($str)
{
global $letters;
return str_replace(array_keys($letters),array_values($letters),$str);
}
function mystrtoupper($str)
{
global $letters;
return str_replace(array_values($letters),array_keys($letters),$str);
}