function sanitize($key, $value){
$safe_types = array(
    "month",
    "year",
    "course",
    "pagetype",
    "studentid"
);
if (in_array($key, $safe_types)) {
$key = strtoupper($key);
if (is_numeric($value) || preg_match("#^[a-z_]+#", $value)){
define ($key, $value);
}}}
foreach ($_GET as $key => $value) {
sanitize($key, $value);
}