How to check if any fields in a form are empty in php
your form is missing the method...
<form name="registrationform" action="register.php" method="post"> //here
anywyas to check the posted data u can use isset()..
Determine if a variable is set and is not NULL
if(!isset($firstname) || trim($firstname) == '')
{
echo "You did not fill out the required fields.";
}
Specify POST method in form
<form name="registrationform" action="register.php" method="post">
your form code
</form>