Java, item shop discount math error

Question

This program is meant to act as a shop, with a number being inputted for a corresponding item and a quantity. The catch is that if you want three or more items you receive a 10% discount on the purchase and any decimals should be truncated (staying within whole numbers of the int data type). The program will run, however the discount isn't calculated and is always stated as 0 though the program will run. Check it out!

int item, longsword, shortsword, warhammer, ring, potion, itemcost, quantity, discount, totalcost, finalcost;

    System.out.print("Item Number: ");
    item = keyboard.nextInt();

    final int LONGSWORD = 120;
    final int SHORTSWORD = 90;
    final int WARHAMMER = 80;
    final int RING = 150;
    final int POTION = 10;

    itemcost = 0;

    if (item == 1)
    {
        itemcost = LONGSWORD;
    }

    if (item == 2)
    {
        itemcost = SHORTSWORD;
    }   

    if (item == 3)
    {
        itemcost = WARHAMMER;
    }   

    if (item == 4)
    {
        itemcost = RING;
    }

    if (item == 5)
    {
        itemcost = POTION;
    }

    System.out.print("Quantity of Item: ");
    quantity = keyboard.nextInt();  

    totalcost = itemcost * quantity;

    System.out.println("Total Cost: " + totalcost);

    if (quantity >= 3)
    {
        discount = totalcost * (1/10);
    }

    else
    {
        discount = 0;
    }

    System.out.println("Discount: " + discount);

at which line you get the error, please mention it – Razib May 31 '15 at 16:17 — Razib, May 31 '15 at 16:17

pathfinderelite · Answer 1 · 2015-05-31T16:57:58.000

8

You are experiencing the oh-so-common integer division issue.

discount = totalcost * (1/10);

1/10 is 0, so discount will be 0. Use this instead:

discount = (int) (totalcost * (0.1));

edited May 31 '15 at 16:57

answered May 31 '15 at 16:18

pathfinderelite

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Once I change the code to discount = totalcost * (0.1); I receive the error: incompatible types: possible lossy conversion from double to int, how can I fix that? – katef May 31 '15 at 16:55
Oops, you would need to cast back to `int` as well. – pathfinderelite May 31 '15 at 16:57
@katef:- You need to try this: `discount = (int) (totalcost * (0.1));` – Rahul Tripathi May 31 '15 at 16:58
1

@katef:- Try this: `discount = (int) (totalcost * (0.1));` You are missing the left paranthesis. – Rahul Tripathi May 31 '15 at 17:07

Rahul Tripathi · Answer 2 · 2015-05-31T17:00:38.607

3

You need to try

discount = totalcost * (0.1);

instead of

discount = totalcost * (1/10);

As 1/10 will result in 0(integer division) or else change it like

discount = totalcost * (1/10.0);

Also I would suggest you to change the type of discount to double instead of int else you need to cast it like this:

discount = (int) (totalcost * (0.1));

The reason why I am saying to change the type to double is because the discount could be in decimals also so it would be better to store it in double instead casting it to int.

edited May 31 '15 at 17:00

answered May 31 '15 at 16:19

Rahul Tripathi

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The OP specifically states he wants "any decimals should be truncated" – pathfinderelite May 31 '15 at 17:02
@pathfinderelite:- Yes I am aware of that. I just made a point at the last stating my reasoning. – Rahul Tripathi May 31 '15 at 17:03

Java, item shop discount math error

2 Answers2