Live ORACLE

DECLARE
 acct_type  INTEGER := 7;
BEGIN
 IF acct_type NOT IN (1,2,3) THEN
   RAISE invalid_number; -- raise predefined exception
 END IF;
EXCEPTION
 WHEN invalid_number THEN
   dbms_output.Put_line('HANDLING INVALID INPUT BY ROLLING BACK.');
   ROLLBACK;
END;
/  

HANDLING INVALID INPUT BY ROLLING BACK.

PL/SQL procedure successfully completed.

Using RAISE to Force a Pre-Defined Exception