Checked / unchecked error messages

On one of my pages if both checkboxes are checked this error message will show up:

            if ($_POST['promote']['multicity_co'] && $_POST['promote']['multicity_cf'])
                $err .= "&bull; please, select only ONE paid promotion<br>";

Code (markup):

My question is, what code should I use to give an error message if NONE of the checkboxes are checked?


Thank you in advance.

 

www.PHP.NET/empty
www.PHP.NET/isset

 

EricBruggema thank you for your help.

 

I'd change your existing code so that checking one checkbox unchecks the other.

 

This is that error msg if non of boxes are checked.

 

You can use isset function to check whether variable is set or not for the checkboxes when you dont check $_POST wont read variable so you should use isset function