In joomla How to Check if user is logged in or not

Use the code below to check if a user is logged in. This is useful if you want to only show certain parts of your component to registered users and not non-registred users. Have fun.

$user =& JFactory::getUser();

if($user->id)

{

    //do user logged in stuff

}

else

{

    //do user not logged in stuff

}