php - warning: division by zero

I am using the following static method for sending mail alerts, but its throwing an error: warning:division by zero ...

Postman::MailAlert($_POST['email'],'Hello '.$_POST['name'].', Thanks for signing up.Your customer id is '.$_POST['city']/'/'.$product_id.'.');

I have solved this issue by putting @, but why is this issue raised, and what am I doing wrong?

Answer

Just the problem part:

$_POST['city']/'/'.$product_id.'.');

Need to change like this.

$_POST['city'] . '/'.$product_id.'.');