Loop - Two Variables (username / Password) Not Clearing Out?

The idea of the program below is to create a sql "module" (just a .sql file) that will loop and ask for a user id until the user enters the correct one. Here is the code I have thusfar:

set serveroutput on;
accept username prompt 'Enter user name here: ';
accept password prompt 'Enter password here: ';

declare
usernameCONFIRM VARCHAR(30);
passwordCONFIRM VARCHAR(30);
begin
select USERID into usernameCONFIRM from GAMEUSER where USERID = '&username';

[code]...

The main problem I'm seeing is that the two variables I ask for (username and password) aren't clearing out.