Thread: Simple CashRegister program behaviour issue [Basic]

Hello,

I am writing a simple Java code, which acts like a Cash Register, However I have faced an issue which I hope to get some help on.

The program:

 
public class TestItem
{
 
 
  private double Order;   // instant variable which will be representing the item's price
  private double Paid;   // Paid is an instant variable which represent the amount paid for the item
 
/**
 * Constructs a Cash Register with zero values
 */
  public TestItem()
  {
      Order = 0;
      Paid = 0;
    }
 
/**
 * Initiating the price of the item ordered in the cash register
 * @param total is the price of the item
 */   
    public void recordOrder(double total)
    {
        this.Order = Order + total;
    }
 
/**
* Deposit the amount paid by the costumer to the cash registrer
* @param dollars is the amount paid
*/
    public void enterPaidValue(double dollars)
    {
        Paid = dollars;
 
    }
 
/**
 * Calculate then return the change to the cosutmer
 */   
    public double giveChange()
    {
 
        double change = Paid - Order;    
        Order = 0;  // after the calculation is done, reset the register value, ready to serve a new costumer
        Paid = 0;   // after the calculation is done, reset the register value, ready to serve a new costumer[/COLOR]
        return change;  // return the change
 
    }
}

Well yes it is easy as it looks, now after coding the tester program:

/**
 * This class is a tester class
 */
 
public class TestItemTester
{
/**
 * Main method.
 */
  public static void main(String[] args)
{
 
   TestItem register = new TestItem();  // creating a new object of the class TestItem
   register.recordOrder(19.93);        // calling the method recordOrder and initiating parameters, this is
                                       // the cost of the Item.
   register.enterPaidValue(20);       // calling the method enterPaidValue, initiating parameter, this is 
                                       // the amount that the costumer have paid.[/COL
 
   System.out.print("Change: ");     
   System.out.println(register.giveChange());  // calling giveChange method to pring out the change.
}
 
}

Everything is going smooth, except of the result of giveChange() method, after calling giveChange() method the result turns out to be: "Change: 0.07000000000000028", I know this is happening becuase of the behaviour of the primitive type "double", which is basicly occuring the (rounding error).

I am trying to result a better output, like "0.07" instead of "0.07000000000000028" as this will confuse the cashier, any thoughts?

Regards,

Originally Posted by KevinWorkman

Do a google search of an article called "what every computer scientist should know about floating point arithmetic". Read it.

You shouldn't use floats (or doubles) for currency. Use an int and count the smallest unit (pennies) then figure it out from there.

You could also use a class like DecimalFormat.

I was asked to use double, thanks anyway.

PS: having a rough day?

I found a very useful website that has a lot of information about formatting what you want to print out. There is specifically a section about formatting floating point numbers, which you should find very helpful Enjoy

A printf format reference page (cheat sheet) | printf reference for java perl ruby | devdaily.com

Originally Posted by Parranoia

I found a very useful website that has a lot of information about formatting what you want to print out. There is specifically a section about formatting floating point numbers, which you should find very helpful Enjoy

A printf format reference page (cheat sheet) | printf reference for java perl ruby | devdaily.com

You sir, are a life saver , this is the kind of solution I was looking for, I edited the last line in the TestItemTester class as follows:

System.out.printf("%8.2f", register.giveChange());

output results: 0.07

Thank you very much you provided me a 2 minutes solution