Displaying the wrong results

[aplaceatthesun]

Hi
I'm attempting the following code to calculate how many quarters, dimes, nickels and pennies a user should get as change, and display them in four labels, when buying an item from a machine. The user inserts the amount paid and the cost of the item in two textboxes.
My code is as follows:

 
Private Sub btnCalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
        ' Variables for fields
        Dim lblCost As Double = CDbl(txtCostItm.Text)
        Dim lblAmnt As Double = CDbl(txtAmntGvn.Text)


        ' Find Difference between Cost of Item and Price Received
        Dim temp As Double = txtAmntGvn.Text - txtCostItm.Text

        'Declare Integers

        Dim lblQuar As Integer
        Dim lblDim As Integer
        Dim lblNick As Integer
        Dim lblPenn As Integer

      


        'How many quarters will be handed
        lblQuar = CInt(temp / 25)
        temp = temp - CDbl(CDbl(lblQuar) * 25)
        lblQrts.Text = lblQuar.ToString

        'Dimes 
        lblDim = CInt(temp / 10)
        temp = temp - CDbl(CDbl(lblDim) * 10)
        lblDimes.Text = lblDim.ToString

        'Nickels 
        lblNick = CInt(temp / 5)
        temp = temp - CDbl(CDbl(lblNick) * 5)
        lblNckls.Text = lblNick.ToString

        'Pennies
        lblPenn = CInt(temp / 1)
        temp = temp - CDbl(CDbl(lblPenn) * 1)
        lblPennies.Text = lblPenn.ToString

I cant understand where I'm going wrong... anyone?!
Thanks a lot, in advance.

[satanorz]

Try using mod & truncate division. Also the code will only work if the difference amount is specified in pennies

        Dim lblCost As Double = CDbl(Txtcostitm.Text)
        Dim lblAmnt As Double = CDbl(txtAmntGvn.Text)

        ' Find Difference between Cost of Item and Price Received
        Dim temp As Double = txtAmntGvn.Text - Txtcostitm.Text

        'How many quarters will be handed
        lblQrts.Text = Math.Truncate(temp / 25)
        temp = temp Mod 25

        'Dimes 
        lblDimes.Text = Math.Truncate(temp / 10)
        temp = temp Mod 10

        'Nickels 
        lblNckls.Text = Math.Truncate(temp / 5)
        temp = temp Mod 5

        'Pennies
        lblPennies.Text = temp

Maybe you've to change something, buy hope it helps as a base.

[makdu]

If there is a decimal expected in the calcuation result, then the integer variable will ignore it. Put break point and step through the program to see where you are going wrong?

[Oblio]

        Debug.WriteLine("Calculate Change")
        Dim decAMT As Decimal = 0.73D 'change
        Dim dec25, dec10, dec5, dec1 As Decimal 'quarters, dimes,nickles, pennies
        'calculate change for amount using Decimal
        dec25 = Math.Floor(decAMT / 0.25D)
        decAMT -= dec25 * 0.25D
        dec10 = Math.Floor(decAMT / 0.1D)
        decAMT -= dec10 * 0.1D
        dec5 = Math.Floor(decAMT / 0.05D)
        decAMT -= dec5 * 0.05D
        dec1 = Math.Floor(decAMT / 0.01D)
        decAMT -= dec1 * 0.01D
        Debug.WriteLine("Pennies " & dec1) 'should be 3
        Debug.WriteLine("Nickles " & dec5)
        Debug.WriteLine("Dimes " & dec10)
        Debug.WriteLine("Quarters " & dec25)
        Debug.WriteLine(decAMT) 'should be 0

[Marraco]

        Debug.WriteLine("Calculate Change")
        Dim decAMT As Decimal = 0.73D 'change
        Dim dec25, dec10, dec5, dec1 As Decimal 'quarters, dimes,nickles, pennies
        'calculate change for amount using Decimal
        dec25 = Math.Floor(decAMT / 0.25D)
        decAMT -= dec25 * 0.25D
        dec10 = Math.Floor(decAMT / 0.1D)
        decAMT -= dec10 * 0.1D
        dec5 = Math.Floor(decAMT / 0.05D)
        decAMT -= dec5 * 0.05D
        dec1 = Math.Floor(decAMT / 0.01D)
        decAMT -= dec1 * 0.01D
        Debug.WriteLine("Pennies " & dec1) 'should be 3
        Debug.WriteLine("Nickles " & dec5)
        Debug.WriteLine("Dimes " & dec10)
        Debug.WriteLine("Quarters " & dec25)
        Debug.WriteLine(decAMT) 'should be 0

I tried to replace Math.Floor with \ division, but it throws a division by zero, even when the divisor is not zero (?).

It was looking simpler to do a class with it, but in the end, it turned more complex:

Option Strict On
Option Explicit On

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim MyCoinChange As New CoinChange

        For Each CoinName As String In MyCoinChange.GetChange(15.16).Keys
            Debug.WriteLine(CoinName.PadRight(9) & ":" & MyCoinChange.GetChange()(CoinName))
        Next CoinName
    End Sub

    Private Class CoinChange
        Friend CoinsValue As New Dictionary(Of String, Double)

        Friend Sub New()
            With CoinsValue
                .Add("Quarters", 25 / 100)
                .Add("Dimes", 10 / 100)
                .Add("Nickles", 5 / 100)
                .Add("Pennies", 1 / 100)
            End With
        End Sub

        Friend ReadOnly Property GetChange(Optional ByVal Mount As Double = Double.NaN) As Dictionary(Of String, Double)
            Get
                Static Answer As Dictionary(Of String, Double)

                If Double.IsNaN(Mount) Then
                    Return Answer
                Else
                    Answer = New Dictionary(Of String, Double)
                End If


                For Each CoinName As String In CoinsValue.Keys
                    Dim CoinCount As Integer

                    CoinCount = CInt(Math.Floor(Mount / CoinsValue(CoinName)))
                    Answer.Add(CoinName, CoinCount)
                    Mount -= CoinCount * CoinsValue(CoinName)
                Next CoinName

                Return Answer

            End Get
        End Property 'GetChange
    End Class 'CoinChange

End Class

The class can also count the remaining coins in the store.

[Oblio]

"I tried to replace Math.Floor with \ division, but it throws a division by zero, even when the divisor is not zero (?)."

That is Integer division so things like 0.05D are getting rounded to ... 0

[Marraco]

"I tried to replace Math.Floor with \ division, but it throws a division by zero, even when the divisor is not zero (?)."

That is Integer division so things like 0.05D are getting rounded to ... 0

Oh. I see.

I were thinking that on this age, any x86 processor contains the "\" operator supported in hardware for any floating point format...

There are so many useless instructions...