Check which user logged in in PHP

Question

I am new in php and I an making an application on iPhone that has a username and password for each user, and users are able to register. I would like to know if there are a lot of users, how can I check which user is logged in ?

When the user logged in their information will be displayed.

I am currently using

if ($id == 1)
{
   //command
}
if ($id == 2)
{
   //command
}
else
   //command

Is there a possible way to check which user is logged in without having to do the if else statement?

Thanks,

Answer 1

I suggest you to keep last user action time in database. Then select users, which did last action, for example, in last 10 minutes and track them as online users.