How to pass username into form that sends data to database

I am trying to pass username to database through form:

[insert_php]
$current_user= wp_get_current_user();
$id= $current_user->user_login; 
[/insert_php]


<input type="hidden" name="id" value="[insert_php]$id[/insert_php]">

But it doesn’t get through, the rest of visible inputs do go through though.