How to place two forms on the same page?

Question

I want to place both register and login form on the same page.
They both starts with:

if (!empty($_POST)) ... 

so, I need something l

Answer 1

You could make two forms with 2 different actions

Or do this

Then you PHP file would work as a switch($_POST['action']) ... furthermore, they can't click on both links at the same time or make a simultaneous request, each submit is a separate request.

Your PHP would then go on with the switch logic or have different php files doing a login procedure then a registration procedure