While loop with If conditions causing unexpected infinite loop

Question

I am revisiting one of my old exercises and I seem to be having problems with my logic. It is a simple console application that is supposed to calculate and display change for a given total and cash tendered. For some reason, I get an infinite loop when I input values which decimal part other than 25.

Here is a screenshot of my console application enter image description here

Here is my code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace James_Archbold_A2
{
    class Program
    {
        static void Main(string[] args)
        {
            double change,total,cash;
            int  fifties = 0, twenties = 0, tens = 0, fives = 0, ones = 0,
                quarters = 0, dimes = 0, nickels = 0, pennies = 0;

            Console.Write("Please enter the total: ");
            total = Convert.ToDouble(Console.ReadLine());

            Console.Write("Please enter the cash tendered: ");
            cash = Convert.ToDouble((Console.ReadLine()));

            change = CalculateChange(total, cash);
            Console.WriteLine(change);

            change *= 100;


            while (change > 0)
            {


                if (change >= 5000)
                {
                    change -= 5000;
                    fifties++;
                    Console.WriteLine(change);


                }

                else if (change >= 2000)
                {
                    change -=2000;
                    twenties++;
                    Console.WriteLine(change);

                }

                else if (change >= 1000)
                {
                    change -=1000;
                    tens++;
                    Console.WriteLine(change);

                }

                else if (change >= 500)
                {
                    change -= 500;
                    fives++;
                    Console.WriteLine(change);
                }

                else if (change >= 100)
                {
                    change -=100;
                    ones++;
                    Console.WriteLine(change);

                }

                else if (change >= 25)
                {
                    change -=25;
                    quarters++;
                    Console.WriteLine(change);

                }

                else if (change >= 10)
                { 
                    change -=10;
                    dimes++;
                    Console.WriteLine(change);
                }

                else if (change >= 5)
                {
                    change -=5;
                    nickels++;
                    Console.WriteLine(change);

                }

                else if (change >= 1)
                {
                    change -=1;
                    pennies++;
                    Console.WriteLine(change);
                }
            }

            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("Total: {0:c}\nCash Tendered: {1:c}" +
                            "\nChange Due: \nFifties: {2}\nTwenties: {3}\nTens: {4}" +
                              "\nFives: {5}\nOnes: {6}\nQuarters: {7}\nDimes: {8}" +
                              "\nNickels: {9}\nPennies: {10}",
                              total, cash, fifties, twenties, tens, fives, ones, quarters, dimes,nickels, pennies);
            Console.WriteLine(sb);
            Console.ReadLine();
        }

        static double CalculateChange(double total, double cash)
        {
            return cash - total;
        }
    }
}

Check your if conditions m while condition – Laxmikant Dange Apr 23 '14 at 01:19 — Laxmikant Dange, Apr 23 '14 at 01:19

score 4 · Accepted Answer · edited May 23 '17 at 12:20

4

If you're writing anything to do with financial calculation, use the decimal data-type. Not double.

I think Jon Skeet's article "Binary floating point and .NET" will give you the greatest insight.

A few other pointers:

Is a double really unsuitable for money?

What Every Computer Scientist Should Know About Floating Point

edited May 23 '17 at 12:20

Community

1
1

answered Apr 23 '14 at 01:23

spender

106,080
28
202
324

It solved most of the problems. Thank you very much. – Jameslat Apr 23 '14 at 01:34

score 1 · Answer 2 · answered Apr 23 '14 at 01:23

1

Make change an int to truncate the .0000000000001 that prevents change from ever falling below 0 with your current algorithm:

int change = CalculateChange(total, cash) * 100;

answered Apr 23 '14 at 01:23

Moho

13,165
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24
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score 0 · Answer 3 · answered Apr 23 '14 at 01:17

0

Use change>=0 in while condition

answered Apr 23 '14 at 01:17

Laxmikant Dange

6,983
4
36
60

1

Not sure if you were the one who downvoted my question, but changing the condition does not change the outcome of the loop. – Jameslat Apr 23 '14 at 01:23
Use Math.floor () to round change in while condition, as you are using double it takes .000000000001 – Laxmikant Dange Apr 23 '14 at 01:36
As a suggestion, don't use double for financial transactions – Laxmikant Dange Apr 23 '14 at 01:39

score 0 · Answer 4 · answered Apr 23 '14 at 01:25

0

You're using doubles for your arithmetic, you can't rely on exact precision for decimal input using doubles.

If you want to use floating points with decimal, you should use C# decimal type.

answered Apr 23 '14 at 01:25

anopse

153
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score 0 · Answer 5 · answered Apr 23 '14 at 01:36

0

In the code snippet provided just round the value of the variable change to its nearest integer and you would get the required output.

From

`while (change > 0)`

to

`while(Math.Round(change)>0)`

Hope this helps

answered Apr 23 '14 at 01:36

Ajay Chauhan

96
3

While loop with If conditions causing unexpected infinite loop

5 Answers5