Italian VAT validation - Validazione della Partita Iva in PLSQL

CREATE OR REPLACE FUNCTION check_pi ( pIva varchar2 )
return integer
is
-- restituisce codice errore
x integer := 0;
y integer := 0;
c integer := 0;
l integer := 0;
z integer := 0;
t integer := 0;
begin
L := length(pIva);
if pIva is NULL then
return 2;
-- argomento nullo
elsif length(pIva) <> 11 then
return 3;
-- lunghezza errata
end if;
DBMS_OUTPUT.PUT_LINE(pIva);
for I in 1..11 loop
c:= TO_NUMBER( substr(pIva, I, 1));
if  REMAINDER(i,2)  = 0 then
y := y + c;
--PARI
if c>=5 then
z := z +1;
end if;
else
x := x + c;
end if;
end loop;
-- DBMS_OUTPUT.PUT_LINE('x=' || to_char(x));
-- DBMS_OUTPUT.PUT_LINE('y=' || to_char(y));
-- DBMS_OUTPUT.PUT_LINE('z=' || to_char(z));
t := (x + (2 * y) + z) ;
if   REMAINDER( t , 10) <>  0 then
return 1;
else
return 0;
end if;
EXCEPTION
WHEN OTHERS
THEN
RETURN -1;
end CHECK_PI;