Routing Question

You could pass the user name to congratulations during the redirect

PHP Code:

redirect(base_url("register/congratulations/$username")); 


Revised congratulations method

PHP Code:

public function congratulations($username)
 {
   $data = array(
     'title'    => 'User successfully registered',
     'username' => $username
   );
   $this->load->view( 'templates/header', $data );
   $this->load->view( 'register/congratulations'); //you don't have to pass $data again if it is unchanged
   $this->load->view( 'templates/footer' );
 }