caracteres deltante en php

<?php

function caracter_alante($cadena, $num_lugares, $caracter){

settype($cadena, "string");

while (strlen($cadena)<$num_lugares){

$cadena = $caracter.$cadena;

}

return $cadena;

}

@$numero=$_POST['numero'];

print '<h1>'.caracter_alante($numero, 3, '0').'</h1>';

?>