Need meaning of an if statement.

[co_ador]

This are set ups values on the top of the page

$submenu = false;
$cat = isset($_GET['subject']) && is_numeric($_GET['subject'])?$_GET['subject']:null;

And this line is within the code and uses those values.

 if($submenu == false && !is_null($cat) && $cat == $row['id'])

What this line means according to the set up values above?

in Special the $submenu variable why does its value needed to be assign to false here and then use it in that conditioned line?

[Bjom]

Just rewrite it and you'll see:

$submenu = false; 
if (isset($_GET['subject'])){
    if (is_numeric($_GET['subject'])){
        $cat=$_GET['subject'];
    } else {
        $cat=null;
    }
}

if submenu has no chance of ever getting set to true elsewhere it is meaningless