Adding additional Joomla registration fields

The default Joomla registration page is very basic. In many situations, one might want to add field to it. This is how to do it:

Just add the fields you want to the following files:

For saving the info

libraries/joomla/database/table/user.php

Display on registration page

components/com_user/views/register/tmpl/default.php 

For updating info

components/com_user/views/user/tmpl/form.php

Backend user form

administrator/components/com_users/views/user/tmpl/form.php