PL/SQL - payment system that dispenses exact change when necessary - oracle

Question

I am currently trying to practice PL/SQL with a new procedure called 'Pay' that recognizes when you pay (based on parameter p_Paid) the amount equal to, less than, or greater than what was needed (based on parameter p_Price).
The difference of p_Price and p_Paid is variable v_Return.
When you pay the exact amount where p_Paid = p_Price, (for example, 10=10) then it should say
"No money to return!"
When you pay (p_Paid) less than what was asked (p_Price), then it should show the text
"You're some short!"
And when you pay (p_Paid) more than what was asked (p_Price), then it should give you change using 20, 10, 5, and 1 dollar bills and indicate the precise number of each type of bill, e.g. if p_Paid was 206 and p_Price was 10, then it should show the difference in exact change:
9 $20 bill(s)
1 $10 bill(s)
1 $5 bill(s)
1 $1 bill(s)
This procedure assumes that everything is an integer (no cents involved).
So far I have managed to get the procedure to recognize when the payment was equal to the price, or less than the price, but I am having a horrible time trying to figure out how to get the money return part to work when they pay more than what was asked for. Any help would be GREATLY appreciated; this is what I have so far (apologies in advance on how convoluted it may seem; I just started learning PL/SQL):
CREATE OR REPLACE procedure Pay
(p_Price IN number,
p_Paid IN number)
AS
v_Return number;
v_20 number;
v_10 number;
v_5 number;
v_1 number;
BEGIN
v_Return := (p_Price - p_Paid);
v_20 := 0;
v_10 := 0;
v_5 := 0;
v_1 := 0;
IF v_Return = 0 THEN
dbms_output.put_line('No money to return!');
ELSE
IF p_Price > p_Paid THEN
dbms_output.put_line('You're some short!');
ELSE
IF p_Price < p_Paid THEN
WHILE v_Return > 20 LOOP
v_Return := v_Return - 20;
v_20 := v_20 + 1;
IF v_Return > 10 THEN
v_Return := v_Return - 10;
v_10 := v_10 + 1;
IF v_Return > 5 THEN
v_Return := v_Return - 5;
v_5 := v_5 + 1;
IF v_Return > 1 THEN
v_Return := v_Return - 1;
v_Return := v_1;
dbms_output.put_line(v_20 || '$20 bill(s)');
dbms_output.put_line(v_10 || '$10 bill(s)');
dbms_output.put_line(v_5 || '$5 bill(s)');
dbms_output.put_line(v_1 || '$1 bill(s)');
END IF;
END IF;
END IF;
END LOOP;
END IF;
END IF;
END IF;
END;
/

Answer 1

There're some errors in your code:
You need to escape that single quote in the You're some short! line, but I guess that's a copy-pasting error.
You're calculating v_Return backwards: you're substracting the payment from the price, so v_Return ends up being negative. Try v_Return := (p_Paid - p_Price);
Half your ENDs are wrongly placed, i.e. the END LOOP; line should be after the v_20 := v_20 + 1; line. Same goes for some of the END IF;s.
The last substraction when v_Return is already less than 5 is not necessary. Just assign the remaining amount to v_1.
And finally, though not an error per se, it's not a good idea to mix conditions, like you're doing using v_Return in the first IF but p_Price and p_Paid in the second and third IFs. If you had used v_Return you would have noticed that you were calculating it backwards since it would have printed "You're some short!" when it shouldn't.
EDIT: And now that you mention it, it's true that because you're checking v_Return > x instead of v_Return >= x, when v_Return is exactly x it won't notice that and will return change in lower units (one $5 and five $1 for $10 of change, instead of just one $10). So just use >=.
So your code should be like this (I tested it and it works OK):
CREATE OR REPLACE procedure Pay
(p_Price IN number,
p_Paid IN number)
AS
v_Return number;
v_20 number;
v_10 number;
v_5 number;
v_1 number;
BEGIN
v_Return := (p_Paid - p_Price);
v_20 := 0;
v_10 := 0;
v_5 := 0;
v_1 := 0;
IF v_Return = 0 THEN
dbms_output.put_line('No money to return!');
ELSE
IF v_Return < 0 THEN
dbms_output.put_line('You''re some short!');
ELSE
WHILE v_Return >= 20 LOOP
v_Return := v_Return - 20;
v_20 := v_20 + 1;
END LOOP;
IF v_Return >= 10 THEN
v_Return := v_Return - 10;
v_10 := v_10 + 1;
END IF;
IF v_Return >= 5 THEN
v_Return := v_Return - 5;
v_5 := v_5 + 1;
END IF;
v_1 := v_Return;
dbms_output.put_line(v_20 || '$20 bill(s)');
dbms_output.put_line(v_10 || '$10 bill(s)');
dbms_output.put_line(v_5 || '$5 bill(s)');
dbms_output.put_line(v_1 || '$1 bill(s)');
END IF;
END IF;
END;
/

Answer 2

Just for fun, here's a more structured version. (The money() function that formats currency amounts and the change() procedure would be better as part of a package, but I've nested them inside the pay() procedure for demo convenience.)
create or replace procedure pay
( p_price pls_integer
, p_paid pls_integer )
as
v_remainder pls_integer := p_paid - p_price;
type change_list is table of pls_integer index by pls_integer;
v_change change_list;
function money
( p_amount pls_integer )
return varchar2
is
begin
return to_char(p_amount,'fmL99999');
end money;
procedure change
( p_amount in out nocopy pls_integer
, p_denomination in pls_integer
, p_change in out nocopy change_list )
is
begin
if p_amount >= p_denomination then
p_change(p_denomination) := trunc(p_amount/p_denomination);
p_amount := mod(p_amount,p_denomination);
else
p_change(p_denomination) := 0;
end if;
dbms_output.put_line
( p_change(p_denomination) || ' ' || money(p_denomination) || ' bill' ||
case when p_change(p_denomination) <> 1 then 's' end );
end change;
begin
if p_paid > p_price then
dbms_output.put_line
( 'Price ' || money(p_price) ||
', Paid ' || money(p_paid) || ': Change due ' || money(v_remainder) || ', as:');
change(v_remainder, 20, v_change);
change(v_remainder, 10, v_change);
change(v_remainder, 5, v_change);
change(v_remainder, 1, v_change);
else
dbms_output.put_line
( case
when p_paid = p_price then 'No change due.'
else 'Please enter an additional ' || money(p_price - p_paid)
end );
end if;
end;
Example:
SQL> exec pay(73, 100)
Price $73, Paid $100: Change due $27, as:
1 $20 bill
0 $10 bills
1 $5 bill
2 $1 bills
SQL> exec pay(73, 50)
Please enter an additional $23
Note it becomes much easier to add a $50 bill.
The four calls to change() could be restructured as a loop, but then you'd have to construct the loop and you don't really gain much.

Answer 3

Please try
v_20 := floor(v_return/20);
tmp:= v_return - v_20*20;
v_10 := floor(tmp/10);
tmp:= v_return - v_20*20 - v_10 * 10;
v_5 := floor(tmp/5);
v_1 := tmp - v_5*5;