2 replies to this topic

[Nokturnal]

Hey guys I'm kinda a novice at programming and I was trying to follow the Cash Register project from the event on this site. I followed one of CommittedC0der's posts where he used a while loop to loop through the array of money types to calculate the amount of change given. I pretty much tried to copy his code exactly like he did it, although I was doing it in Java. However, I'm getting a "java.lang.ArrayIndexOutOfBoundsException: 9" error. I know it has something to do with the while loop..I think..but I can't seem to figure it out. Any help would be appreciated.

import java.util.*;

import java.text.*;


public class Main {


    /**

     * @param args the command line arguments

     */

    public static void main(String[] args) {



        double[] money = {50.00, 20.00, 10.00, 5.00, 1.00, 0.25, 0.10, 0.05, 0.01};

        int i = 0;

        int j = 0;

        double amountDue;

        double amountGiven;

        double change;


        Scanner kbReader = new Scanner(System.in);


        System.out.print("Amount Due: ");

        amountDue = kbReader.nextDouble();


        System.out.print("Amount Given: ");

        amountGiven = kbReader.nextDouble();


        change = (amountGiven - amountDue);


        /*

        NumberFormat fmt = NumberFormat.getNumberInstance();

        fmt.setMaximumFractionDigits(2);

        fmt.setMinimumFractionDigits(2);

        String s = fmt.format(change);

        */ // Rounding off change


        System.out.println("Change: " + change);


        while (change > 0.00) {


            while (change >= money[i]) {


                change -= money[i];

                j++;


            }


            System.out.println(j + " * " + money[i] + " = " + (money[i] * j));

            i++;

            j = 0;


        }


    }


}

[ZekeDragon]

Ahh, welcome to the Floating Point Rounding Demons. Here's your problem, look at what you're doing with the change:

while (change > 0.00) {

  while (change >= money[i]) {

    [b]change -= money[i];[/b]

    j++;

  }

This means you're subtracting a double from another double, successively. Because of floating point rounding, you won't end up with a perfect fractionally 0 value after the math is done, instead you'll end up with a value like "0.000000000001". This IS greater than 0, which means that the while loop executes another time, and attempts to access the money array with too high a value. This causes an exception to be thrown and your program to quit.

To fix this, you can either try doing this with ints, or you can change your while loop condition:

while (change > 0.001)

You're not calculating hay pennies, so you'll be fine.

WARNING: Again, because of floating point, this program may also behave erratically. Remember that when you're performing successive modifications to a float value not to expect it to be precise. Float values are usually used for calculating, for example, the X, Y, and Z locations of an object in 3D space. You should use int's for this, as that will not have any imprecision issues.

[nicckk]

Your array only has 8 indices, as the first index is 0. You're getting the error because you're calling the 9th(non-existent) location in the array.