Variable Problem, I think.

[Joseph Fisher]

I have this program. I'm supposed to calculate change with appropriate coins. I've been over this a bunch and my math and loops seems to be in order. It's just not coming out right. I output the change value to the screen throughout the loops and at some point it gets all wonky. I can't understand why. Can somebody point me in the direction as to why? Thanks.

import java.io.*;
import java.text.*;
import java.math.*;
 
public class Change
{
    public static void main (String[] args) throws IOException
    {
        //Sets up to read input from the keyboard
        BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
 
        //Gets initial input from user 
        System.out.print("Enter the amount due (negative # to exit) -> $");
        String d = read.readLine();
        double due = Double.parseDouble( d );
 
        //Sets appropriate decimal position for currency
        NumberFormat nf = java.text.NumberFormat.getInstance();
        nf.setMinimumFractionDigits(2);
        nf.setMaximumFractionDigits(2);
        while ( due > 0 ) //Continues to loop until a negative number is input
        {
            int dollar = 0;  //Variable declarations
            int quarter = 0;
            int dime = 0;
            int nickel = 0;
            int penny = 0;
            double change = 0;
            System.out.print("Enter the amount tendered -> $");//Get tender input
            String t = read.readLine();
            double tender = Double.parseDouble( t );
            change = tender - due;
            System.out.println("$" + nf.format(change) + " due"); 
            while ( change - 1 >= 0 )//Counts dollar bills
            {
                dollar++;
                change--;
            }
            while ( change - 0.25 >= 0 )//Counts quarters
            {
                quarter++;
                change = change - 0.25;
            }
            while ( change - 0.10 >= 0 )//Counts dimes
            {
                dime++;
                change = change - 0.10;
            }
            while ( change - 0.05 >= 0 )//Counts nickels
            {
                nickel++;
                change = change - 0.05;
            }
            while ( change - 0.01 >= 0 )//Counts pennies
            {
                penny++;
                change = change - 0.01;
            }   
 
            //Output data to user         
            System.out.println("That's " + dollar + " dollars " + quarter + 
                              " quarters " + dime + " dimes " + nickel + 
                              " nickels and " + penny + " pennies.");
            System.out.print("Enter the amount due (negative # to exit) -> $");
            d = read.readLine();
            due = Double.parseDouble( d );
        }
        
    }
}    

[Santhosh Kumar]

I tried couple of cases and it worked fine.

   
Enter the amount due (negative # to exit) -> $ 100.00
Enter the amount tendered -> $ 120.00
$20.00 due
That's 20 dollars 0 quarters 0 dimes 0 nickels and 0 pennies.
Enter the amount due (negative # to exit) -> $ 34.59
Enter the amount tendered -> $87.98
$53.39 due
That's 53 dollars 1 quarters 1 dimes 0 nickels and 4 pennies.
Enter the amount due (negative # to exit) -> $
 

May be you want to post the values, it didn't work?

[Campbell Ritchie]

You do realise you NEVER use floating-point arithmetic for money in real life? You can get some nasty errors when you get values like 1.999999999999999999999999 instead of 2.0.

Were you told you use loops to calculate the change? I would have used the % and / operators, which of course work better using integer arithmetic. Your while(change - 1 >= 0) is an awkward formula.