VB Change Calulator - vb.net

Question

I am creating a VB 2008 change calculator as an assignment. The program is to use the amount paid - the amount due to calculate the total.(this is working fine). After that, it is to break that amount down into dollars, quarters, dimes, nickels, and pennies. The problem I am having is that sometimes the quantity of pennies, nickels or dimes will be a negative number. For example $2.99 = 3 Dollars and -1 Pennies.
SOLVED
Thanks to the responses, here is what I was able to make work with my limited knowledge.
Option Explicit On
Option Strict Off
Option Infer Off
Public Class frmMain
Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
'Clear boxes
lblDollarsAmount.Text = String.Empty
lblQuartersAmount.Text = String.Empty
lblDimesAmount.Text = String.Empty
lblNickelsAmount.Text = String.Empty
lblPenniesAmount.Text = String.Empty
txtOwed.Text = String.Empty
txtPaid.Text = String.Empty
lblAmountDue.Text = String.Empty
txtOwed.Focus()
End Sub
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
'Close application'
Me.Close()
End Sub
Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
' Find Difference between Total Price and Total Received
lblAmountDue.Text = Val(txtPaid.Text) - Val(txtOwed.Text)
Dim intChangeAmount As Integer = lblAmountDue.Text * 100
'Declare Integers
Dim intDollarsBack As Integer
Dim intQuartersBack As Integer
Dim intDimesBack As Integer
Dim intNickelsBack As Integer
Dim intPenniesBack As Integer
' Change Values
Const intDollarValue As Integer = 100
Const intQuarterValue As Integer = 25
Const intDimeValue As Integer = 10
Const intNickelValue As Integer = 5
Const intPennyValue As Integer = 1
'Dollars
intDollarsBack = CInt(Val(intChangeAmount \ intDollarValue))
intChangeAmount = intChangeAmount - Val(Val(intDollarsBack) * intDollarValue)
lblDollarsAmount.Text = intDollarsBack.ToString
'Quarters
intQuartersBack = CInt(Val(intChangeAmount \ intQuarterValue))
intChangeAmount = intChangeAmount - Val(Val(intQuartersBack) * intQuarterValue)
lblQuartersAmount.Text = intQuartersBack.ToString
'Dimes
intDimesBack = CInt(Val(intChangeAmount \ intDimeValue))
intChangeAmount = intChangeAmount - Val(Val(intDimesBack) * intDimeValue)
lblDimesAmount.Text = intDimesBack.ToString
'Nickels
intNickelsBack = CInt(Val(intChangeAmount \ intNickelValue))
intChangeAmount = intChangeAmount - Val(Val(intNickelsBack) * intNickelValue)
lblNickelsAmount.Text = intNickelsBack.ToString
'Pennies
intPenniesBack = CInt(Val(intChangeAmount \ intPennyValue))
intChangeAmount = intChangeAmount - Val(Val(intPenniesBack) * intPennyValue)
lblPenniesAmount.Text = intPenniesBack.ToString
End Sub
End Class

Answer 1

In your example of $2.99, look at where you calculate inDollarsBack. You are obviously getting a value of 3, when you need 2. Without giving it away, think of possible reasons why dividing 2.99 by 1 would produce a value of 3.

Answer 2

You can use the following change calculator and then update the UI.
Imports System.Collections.Generic
Imports System.Linq
Imports Microsoft.VisualBasic
Public Class ChangeCalculator
Private denominations As List(Of Denomination)
Public Sub New()
Me.denominations = New List(Of Denomination)
With Me.denominations
.Add(New Denomination With {.Value = 1D})
.Add(New Denomination With {.Value = 0.25D})
.Add(New Denomination With {.Value = 0.1D})
.Add(New Denomination With {.Value = 0.05D})
.Add(New Denomination With {.Value = 0.01D})
End With
End Sub
Public Sub Calculate(ByVal change As Decimal)
Me.ResetDenominationUnits()
Dim remainingChange = change
For Each denomination In (From d In Me.denominations
Order By d.Value Descending
)
If remainingChange > denomination.Value Then
denomination.Units = CInt(
Conversion.Int(remainingChange / denomination.Value)
)
remainingChange -= denomination.Value * denomination.Units
End If
Next
End Sub
Public ReadOnly Property Dollars As Integer
Get
Return Me.GetUnits(1D)
End Get
End Property
Public ReadOnly Property Quarters As Integer
Get
Return Me.GetUnits(0.25D)
End Get
End Property
Public ReadOnly Property Dimes As Integer
Get
Return Me.GetUnits(0.1D)
End Get
End Property
Public ReadOnly Property Nickels As Integer
Get
Return Me.GetUnits(0.05D)
End Get
End Property
Public ReadOnly Property Pennies As Integer
Get
Return Me.GetUnits(0.01D)
End Get
End Property
Private Function GetUnits(ByVal denomination As Decimal) As Integer
Return (From d In Me.denominations
Where d.Value = denomination
).Single().Units
End Function
Private Sub ResetDenominationUnits()
For Each denomination In Me.denominations
denomination.Units = 0
Next
End Sub
End Class
Public Class Denomination
Public Property Value As Decimal
Public Property Units As Integer
End Class

Answer 3

Inasmuch as my answer's similar to Tim Murphy's, I think this one's more straight forward and you don't need to update the UI.
Module Module1
Sub Main()
Console.WriteLine("Enter the amount of change or type EXIT to close.")
Dim input = Console.ReadLine
Do While input.ToUpper.Trim <> "EXIT"
Dim c = GetChange(CDec(Val(input)))
Console.WriteLine("{0} dollars, {1} quarters, {2} dimes, {3} nickels and {4} pennies", _
c.Dollars, c.Quarters, c.Dimes, c.Nickels, c.Pennies)
Console.WriteLine(vbCrLf & vbCrLf & "Enter the amount of change or type EXIT to quit.")
input = Console.ReadLine
Loop
End Sub
Public Function GetChange(ByVal change As Decimal) As Change
Dim denominations = New Decimal() {1D, 0.25D, 0.1D, 0.05D, 0.01D}
Dim c(4) As Integer
For i = 0 To denominations.Length - 1
If change >= denominations(i) Then
c(i) = CInt(Conversion.Int(change / denominations(i)))
change -= (c(i) * denominations(i))
End If
Next
Dim r As New Change
With r
.Dollars = c(0)
.Quarters = c(1)
.Dimes = c(2)
.Nickels = c(3)
.Pennies = c(4)
End With
Return r
End Function
Public Structure Change
Dim _dollars As Integer
Dim _quarters As Integer
Dim _nickels As Integer
Dim _dimes As Integer
Dim _pennies As Integer
Public Property Dollars() As Integer
Get
Return _dollars
End Get
Set(ByVal value As Integer)
_dollars = value
End Set
End Property
Public Property Quarters() As Integer
Get
Return _quarters
End Get
Set(ByVal value As Integer)
_quarters = value
End Set
End Property
Public Property Dimes() As Integer
Get
Return _dimes
End Get
Set(ByVal value As Integer)
_dimes = value
End Set
End Property
Public Property Nickels() As Integer
Get
Return _nickels
End Get
Set(ByVal value As Integer)
_nickels = value
End Set
End Property
Public Property Pennies() As Integer
Get
Return _pennies
End Get
Set(ByVal value As Integer)
_pennies = value
End Set
End Property
End Structure
End Module

Answer 4

Public Shared Function CalculateChange(ByVal dblDollarsPaid As Double, ByVal dblDollarsOwed As Double)
Dim intChangeCents As Integer
Dim change As New Change()
intChangeCents = CInt((dblDollarsPaid - dblDollarsOwed) * 100)
change.Dollars = intChangeCents \ 100
intChangeCents = intChangeCents Mod 100
change.Quarters = intChangeCents \ 25
intChangeCents = intChangeCents Mod 25
change.Dimes = intChangeCents \ 10
intChangeCents = intChangeCents Mod 10
change.Nickels = intChangeCents \ 5
intChangeCents = intChangeCents Mod 5
change.Pennies = intChangeCents
Return change
End Function
Usage:
Dim c As Change
c = CalculateChange(13.26, 2.99)
Console.WriteLine("{0} dollars, {1} quarters, {2} dimes, {3} nickels and {4} pennies", _
c.Dollars, c.Quarters, c.Dimes, c.Nickels, c.Pennies)
\ is the operator for integer division, e.g. 5 \ 2 is 2, not 2.5.
The Change structure is from Alex Essilfie's answer.

Answer 5

Quite Simply, here it is. To solve the negative change, remove all Options except Explicit
Option Explicit On
Public Class frmMoneyChange
Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
lblFivesAmount.Text = String.Empty
lblTensAmount.Text = String.Empty
lblDollarsAmount.Text = String.Empty
lblQuartersAmount.Text = String.Empty
lblDimesAmount.Text = String.Empty
lblNickelsAmount.Text = String.Empty
lblPenniesAmount.Text = String.Empty
txtOwed.Text = String.Empty
txtPaid.Text = String.Empty
lblAmountDue.Text = String.Empty
txtOwed.Focus()
End Sub
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
Me.Close()
End Sub
Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
Dim decChangeAmount As Decimal
Dim intDollarsBack As Integer
Dim intQuartersBack As Integer
Dim intDimesBack As Integer
Dim intNickelsBack As Integer
Dim intPenniesBack As Integer
Dim decPaid As Decimal
Dim decOwed As Decimal
Const intFiveDollarValue As Integer = 5
Const intTenDollarValue As Integer = 10
Const intDollarValue As Integer = 1
Const decQuarterValue As Decimal = 0.25
Const decDimeValue As Decimal = 0.1
Const decNickelValue As Decimal = 0.05
Const decPennyValue As Decimal = 0.01
decOwed = Convert.ToDecimal(txtOwed.Text)
decPaid = Convert.ToDecimal(txtPaid.Text)
decChangeAmount = decPaid - decOwed
lblAmountDue.Text = decChangeAmount.ToString("C")
'Ten Dollars
intDollarsBack = (decChangeAmount * 100 \ intTenDollarValue * 100)
decChangeAmount = decChangeAmount - (intDollarsBack) * intTenDollarValue
lblTensAmount.Text = intDollarsBack.ToString
'Five Dollars
intDollarsBack = (decChangeAmount * 100 \ intFiveDollarValue * 100)
decChangeAmount = decChangeAmount - (intDollarsBack) * intFiveDollarValue
lblFivesAmount.Text = intDollarsBack.ToString
'Dollars
intDollarsBack = (decChangeAmount * 100 \ intDollarValue * 100)
decChangeAmount = decChangeAmount - (intDollarsBack) * intDollarValue
lblDollarsAmount.Text = intDollarsBack.ToString
'Quarters
intQuartersBack = (decChangeAmount * 100 \ decQuarterValue * 100)
decChangeAmount = decChangeAmount - (intQuartersBack) * decQuarterValue
lblQuartersAmount.Text = intQuartersBack.ToString()
'Dimes
intDimesBack = (decChangeAmount * 100 \ decDimeValue * 100)
decChangeAmount = decChangeAmount - (intDimesBack) * decDimeValue
lblDimesAmount.Text = intDimesBack.ToString
'Nickels
intNickelsBack = (decChangeAmount * 100 \ decNickelValue * 100)
decChangeAmount = decChangeAmount - (intNickelsBack) * decNickelValue
lblNickelsAmount.Text = intNickelsBack.ToString
'Pennies
intPenniesBack = (decChangeAmount * 100 \ decPennyValue * 100)
decChangeAmount = decChangeAmount - (intPenniesBack) * decPennyValue
lblPenniesAmount.Text = intPenniesBack.ToString
End Sub
End Class