if a client form is filled out but there EEE is not filled out and i visit there page... how can i write a variable that says ... check the field 'EEENUMBER' in the input and if it's blank than echo an alert Must have EEE NUMBER...

PHP Code:
<tr><td>EEE</td><td><?php inp('EEENUMBER'); ?></td></tr> <?php if ($EEENUMBER <= 0) {
    echo 
"Must have EEE NUMBER.";
}
?>

please help on this easy task.. I've gone brain dead today. Thanks in adavance.