create or replace procedure SP_H05_04 is
  v_bankrek number;
  
  function geldig_bankrek
  (p_bankrek in varchar2)
  
  return varchar2
   is
     v_loop varchar2;
     v_terug varchar2;
     i_getal number;
     e_niet_negen exception;
  begin
  
  if length(p_bankrek) != 9
    then
      raise e_niet_negen;
  end if;
  
  v_getal := 9;

  for i in 1 .. length(p_bankrek)
  loop
    v_terug := v_terug + (v_getal * substr(v_terug, i, 1));
    v_getal := v_getal -1;
  end loop;
  
  exception
  when e_niet_negen
    then
      raise_application_error(-20000, 'Nee!');
  
  end geldig_bankrek;
  
begin
end;