[Urgent] Very Simple PHP Question

Hey,

I feel like an idiot asking this, but my mind has gone blank, and its very annoying.

How do i check what a user has entered in a form against some preset values?

I have a drop down with 5 options and i want to make sure the person is using my form by checking they have chosen one of those 5 options and not something else.

Thanks

 

$allowed = array('one value','another value','pie','cheese');
if ( ! in_array($_POST['selectname'],$allowed) ) {
    echo 'Not allowed';
}

PHP:

 

Thanks, its all come rushing back