How to make an inputbox and text file appear in Visual Basic? - vb.net

Question

I'm making a program that allows users to see information on songs, play an excerpt of them, and purchase selected ones.
And allow users to click the Purchase button to buy the indicated tune.
When checking out:
Users cannot checkout if they have not purchased any tunes, however they can exit the program.
Use an InputBox so that users can enter their sales tax rate. Since users are entering a value, you must perform data validation on their input.
Allow users to cancel the check out process by clicking the InputBox Cancel button.
When the input box is displayed, the textbox should have the focus, and when an incorrect tax value is added, the incorrect value should be cleared and the textbox should have focus again.
Use Write/Writeline to create a purchase order text file named PurchaseOrder.txt that includes the date the file was created and an itemized list of purchases, the subtotal, tax, and total.
When I click on the "Purchase" button of the selected song and click on the "Check Out" button, I get an error that say: "You have not ordered any items". Please refer to the cmdCheckOut_Click subroutine in the code below. I think that's where I'm getting my errors.
Here's the code:
Public Structure musicInfo
<VBFixedString(30)> Public title As String
<VBFixedString(20)> Public artist As String
<VBFixedString(20)> Public genre As String
<VBFixedString(10)> Public duration As String
Public year As Integer
Public price As Double
<VBFixedString(15)> Public songFileName As String
End Structure
Public Const NoOfTunes = 5
Public songs(NoOfTunes - 1) As musicInfo
Option Explicit On
Imports System.IO
Public Class frmTunes
Public index As Integer
Public purchaseCount As Integer
Public purchasePrice(10) As Decimal
Public purchaseTitle(10) As String
Private Sub frmTunes_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim i As Integer
FileOpen(1, "music.dat", OpenMode.Random, , , Len(songs(0)))
For i = 0 To NoOfTunes - 1
FileGet(1, songs(i))
Next
FileClose(1)
cmdPrevious.Visible = False
DisplaySong(0)
End Sub
Sub DisplaySong(ByVal i As Int32)
lblTitle.Text = songs(i).title
lblArtist.Text = songs(i).artist
lblGenre.Text = songs(i).genre
lblDuration.Text = songs(i).duration
lblYear.Text = Convert.ToString(songs(i).year)
lblPrice.Text = Convert.ToString(songs(i).price)
End Sub
Private Sub cmdStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdStop.Click
My.Computer.Audio.Stop()
End Sub
Private Sub cmdPurchase_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPurchase.Click
purchaseTitle(purchaseCount) = lblTitle.Text
purchasePrice(purchaseCount) = Convert.ToDecimal(lblPrice.Text)
purchaseCount = (purchaseCount + 1)
End Sub
Private Sub cmdPrevious_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPrevious.Click
index = (index - 1)
If (index < 4) Then
cmdNext.Visible = True
End If
If (index = 0) Then
cmdPrevious.Visible = False
End If
DisplaySong(index)
End Sub
Private Sub cmdNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdNext.Click
index = (index + 1)
If (index = NoOfTunes - 1) Then
cmdNext.Visible = False
End If
If (index > 0) Then
cmdPrevious.Visible = True
End If
DisplaySong(index)
End Sub
Private Sub cmdPlay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPlay.Click
My.Computer.Audio.Play(songs(index).songFileName)
End Sub
Private Sub cmdCheckOut_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdCheckOut.Click
Dim decimal1 As Decimal
Dim decimal3 As Decimal
Dim decimal4 As Decimal
Dim str1 As String = ""
If (Not purchaseCount) Then
MsgBox("You have not ordered any items!", MsgBoxStyle.Exclamation, "Order Error")
Else
Do While ((IsNumeric(str1) Or (Decimal.Compare(decimal3, Decimal.Zero) < 0)) Or (Decimal.Compare(decimal3, (10D)) > 0))
str1 = InputBox("Enter your tax rate as a % between and including 0 - 10:", "Tax Rate", "", -1, -1)
If (str1 <> "") Then
If (Not IsNumeric(str1)) Then
MsgBox("You must enter a numeric tax rate", MsgBoxStyle.Exclamation, "Tax Rate Error")
Else
Dim dec3 As Decimal = Convert.ToDecimal(str1)
If ((Decimal.Compare(decimal3, Decimal.Zero) < 0) Or (Decimal.Compare(decimal3, (10D)) > 0)) Then
MsgBox("You must enter a tax rate between and including 0% - 10%", MsgBoxStyle.Exclamation, "Tax Rate Error")
End If
End If
End If
Loop
Dim StreamWriter As StreamWriter = File.CreateText("PurchaseOrder.txt")
StreamWriter.WriteLine("For Purchases dated: " & DateTime.Now.ToLongDateString())
StreamWriter.WriteLine()
Dim num2 As Integer = (purchaseCount - 1)
Dim num1 As Integer = 0
Do While (num1 <= num2)
StreamWriter.Write(Strings.FormatCurrency(CType(Me.purchasePrice(num1), Decimal) & " "))
StreamWriter.WriteLine(Me.purchaseTitle(num1))
Dim dec1 As Decimal = Decimal.Add(Nothing, Me.purchasePrice(num1))
num1 = (num1 + 1)
Loop
StreamWriter.WriteLine("------")
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal1, Decimal) & " Subtotal"))
Dim decimal2 As Decimal = New Decimal(((Convert.ToDouble(decimal3) * 0.01) * Convert.ToDouble(decimal1)))
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal2, Decimal) & " Tax"))
StreamWriter.WriteLine("------")
Dim dec4 As Decimal = Decimal.Add(decimal1, decimal2)
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal4, Decimal) & " Total"))
MsgBox("Purchase Order has been created", MsgBoxStyle.OkOnly)
StreamWriter.Close()
Me.Close()
End If
End Sub
End Class

Answer 1

Not doesn't do what you think it does. In VB.Net the Not operator performs a bitwise invert on non-boolean value. So if purchaseCount = 1 then Not purchaseCount = 0xFFFFFFFE = -2, which with convert to True. Only an integer value of 0, whould convert to false.
Change the test If (Not purchaseCount) to If (purchaseCount = 0)