can't redefine a variable?

[Sabmin]

maybe this is a stupid question but I don't get it...

echo $user->user;

 

works but why doesn't:

 

Code:
$username = $user->user;
echo $username;

or at least how can I send this variable through a url into an iframe?

a simple

$var = ("url.php?user=" . $user->user);

just returns a empty string.