exception errors

I am beginning to use exceptions in visual basic and haveing issues with my compute button(totals button works fine). My issue is I have a group box of customer information and the customer name, shipping address, and telephone cannot be blank and just need help on how I can throw exception with this. I also have a purchase information group box that checks to make sure product identifier, purchase price, and quantity purchased are not blank either. I was able to get this to work fine for purchase price and quantity purchased but does not work for product identifier. If someone could please walk me through this so I hopefully wont have to ask how to do exceptions again. Here is my code and if I need to explain anything better please let me know...

Code:

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Public Class Form1

    'Declare module level variables
    Private totalDiscountDecimal As Decimal
    Private totalQuantityInteger As Integer

    Private Sub computeButton_Click(sender As Object, e As EventArgs) Handles computeButton.Click
        'Begin try statement to check for errors
        Try

            'Declare constant for sales tax
            Const SALES_TAX As Single = 0.05
            Const FED_EX_AIR As Single = 25.0
            Const FED_EX_GROUND As Single = 20.0
            Const US_POSTAL As Single = 12.0
            Const ONE_YEAR_WARRANTY As Single = 75.0
            Const CLUB_MEMBERSHIP As Single = 150.0
            Const TIRE_SALE As Single = 25.0
            Const WHOLESALE_DISCOUNT As Single = 0.1
            Const RETAIL_DISCOUNT As Single = 0.0

            'Declare variables
            Dim subtotalDecimal, totalDueDecimal, salesTaxDecimal, shippingCostDecimal, oneYearWarrantyDecimal,
            extrasDecimal, clubMembershipDecimal, tireSaleDecimal, discountDecimal As Decimal


            'Declare variables and convert values from textbox controls to memory
            Dim purchasePriceDecimal As Decimal = Decimal.Parse(purchasePriceTextBox.Text, Globalization.NumberStyles.Currency)
            Dim quantityPurchasedInteger As Integer = Integer.Parse(quantityPurchasedTextBox.Text, Globalization.NumberStyles.Number)


            'Determine the shipping cost if fed ex air is clicked
            If fedExAirRadioButton.Enabled Then
                shippingCostDecimal = FED_EX_AIR
            ElseIf fedExGroundRadioButton.Enabled Then
                shippingCostDecimal = FED_EX_GROUND
            ElseIf USPostalRadioButton.Enabled Then
                shippingCostDecimal = US_POSTAL
            End If

            'Calculate total shipping cost
            shippingCostDecimal *= quantityPurchasedInteger

            'Show the results in a textbox
            shippingCostTextBox.Text = shippingCostDecimal

            'Check extras
            If oneYearWarrantyCheckBox.Checked Then
                oneYearWarrantyDecimal = ONE_YEAR_WARRANTY
            End If
            If clubMembershipCheckBox.Checked Then
                clubMembershipDecimal = CLUB_MEMBERSHIP
            End If
            If tireSaleCheckBox.Checked Then
                tireSaleDecimal = TIRE_SALE
            End If

            'Determine extrasDecimal
            extrasDecimal = oneYearWarrantyDecimal + clubMembershipDecimal + tireSaleDecimal

            'Determine the discount
            If wholesaleRadioButton.Checked Then
                discountDecimal = (purchasePriceDecimal * quantityPurchasedInteger) * WHOLESALE_DISCOUNT

            ElseIf retailRadioButton.Checked Then
                discountDecimal = RETAIL_DISCOUNT
            End If

            subtotalDecimal = purchasePriceDecimal * quantityPurchasedInteger + shippingCostDecimal + extrasDecimal - discountDecimal

            'Determine the sales tax
            If wholesaleRadioButton.Checked Then
                salesTaxDecimal = 0.0
            ElseIf retailRadioButton.Checked Then
                salesTaxDecimal = subtotalDecimal * SALES_TAX
            End If

            'Determine the total due
            totalDueDecimal = subtotalDecimal + salesTaxDecimal


            'Display output in textboxes
            salesTaxTextBox.Text = salesTaxDecimal.ToString("C")
            subtotalTextBox.Text = subtotalDecimal.ToString("C")
            shippingCostTextBox.Text = shippingCostDecimal.ToString("C")
            costOfExtrasTextBox.Text = extrasDecimal.ToString("C")
            discountTextBox.Text = discountDecimal.ToString("C")
            totalDueTextBox.Text = totalDueDecimal.ToString("C")


            'Enable\Disable buttons
            computeButton.Enabled = False
            resetButton.Enabled = True

            'Accumulate totals
            totalDiscountDecimal += discountDecimal
            totalQuantityInteger += quantityPurchasedInteger

        Catch ex As Exception
            MessageBox.Show("Product identifier, purchase price, or quantity purchased has not been entered!",
                            "Customer name error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

    End Sub

    Private Sub totalCountAverageButton_Click(sender As Object, e As EventArgs) Handles totalCountAverageButton.Click
        'Try statement to check for errors
        Try
            'Determine the average Discount
            Dim averageDiscountDecimal = totalDiscountDecimal / totalQuantityInteger

            'Display totals in a message string
            Dim messageString As String = "Total Wholesale Discounts: " & totalDiscountDecimal.ToString("C") &
                                        ControlChars.NewLine & "Total Wholesale Quantity Sold: " & totalQuantityInteger.ToString("N0") &
                                        ControlChars.NewLine & "Average Discount Amount: " & averageDiscountDecimal.ToString("C")

            'Display a header for the message string
            MessageBox.Show(messageString, "Totals, Counts and Averages", MessageBoxButtons.OK, MessageBoxIcon.Information)

        Catch exArithmeticException As ArithmeticException
            MessageBox.Show("No products have been sold yet", "Zero Sales Message", MessageBoxButtons.OK, MessageBoxIcon.Information)

        Catch ex As Exception
            MessageBox.Show("Unexpected error - inform the system administrator", "Unknown error in totals",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try
    End Sub

    Private Sub resetButton_Click(sender As Object, e As EventArgs) Handles resetButton.Click
        'Clear the textboxes
        customerNameTextBox.Clear()
        shippingAddressTextBox.Clear()
        telephoneMaskedTextBox.Clear()
        productIdentifierTextBox.Clear()
        purchasePriceTextBox.Clear()
        quantityPurchasedTextBox.Clear()
        shippingCostTextBox.Clear()
        costOfExtrasTextBox.Clear()
        discountTextBox.Clear()
        subtotalTextBox.Clear()
        salesTaxTextBox.Clear()
        totalDueTextBox.Clear()

        'Set radio buttons back to default
        wholesaleRadioButton.Checked = True
        fedExAirRadioButton.Checked = True

        'Uncheck all the extras checkboxes
        oneYearWarrantyCheckBox.Checked = False
        clubMembershipCheckBox.Checked = False
        tireSaleCheckBox.Checked = False

        'Set the focus to the customer name textbox
        customerNameTextBox.Focus()

        'Enable\disable buttons
        computeButton.Enabled = True
        resetButton.Enabled = False
    End Sub

    Private Sub exitButton_Click(sender As Object, e As EventArgs) Handles exitButton.Click
        'Exit the program with being prompted to exit
        Dim response As Integer
        response = MessageBox.Show("Do you want to close the form?", "Quit?", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2)

        If response = vbYes Then
            Me.Close()
        End If
    End Sub

End Class

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You don't need to use EXCEPTION HANDLING for that. That is more for system errors, not program errors. Just check if the field(s) are BLANK or NOTHING, and set a flag for each one. Set it FALSE before the checks, and if there is ANY error, each one can set it to TRUE. Check for TRUE before executing the code which might cause the exception. Of course, if there is any chance of a missing CD or Network Share, then, use and EXCEPTION. ON ERROR XXX

Here's a quick sample:

Code:

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Public Function DigestFileToHS(InFile As String) As String
On Error GoTo errorhandler
GoSub begin

errorhandler:
    DigestFileToHexStr = ""
    Exit Function
   
begin:
    Dim FileO As Integer
    FileO = FreeFile
    Call FileLen(InFile)
    Open InFile For Binary Access Read As #FileO
    MD5Init
    Do While Not EOF(FileO)
        Get #FileO, , ByteBuffer
        If Loc(FileO) < LOF(FileO) Then
            ByteCounter = ByteCounter + 64
            MD5Transform ByteBuffer
        End If
    Loop
    ByteCounter = ByteCounter + (LOF(FileO) Mod 64)
    Close #FileO
    MD5Final
    DigestFileToHS = GetValues
End Function

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I am only in chapter 4 on this visual basic book so the code below is way over my head as this stage lol.

I kind of messed around with it alittle and I do get an error to come up now with the code below but the only issue is aftern the error does come up the program still computer the totals...

Code:

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Public Class Form1

    'Declare module level variables
    Private totalDiscountDecimal As Decimal
    Private totalQuantityInteger As Integer

    Private Sub computeButton_Click(sender As Object, e As EventArgs) Handles computeButton.Click
        'Begin try statement to check for errors
        Try

            'Declare constant for sales tax
            Const SALES_TAX As Single = 0.05
            Const FED_EX_AIR As Single = 25.0
            Const FED_EX_GROUND As Single = 20.0
            Const US_POSTAL As Single = 12.0
            Const ONE_YEAR_WARRANTY As Single = 75.0
            Const CLUB_MEMBERSHIP As Single = 150.0
            Const TIRE_SALE As Single = 25.0
            Const WHOLESALE_DISCOUNT As Single = 0.1
            Const RETAIL_DISCOUNT As Single = 0.0

            'Declare variables
            Dim subtotalDecimal, totalDueDecimal, salesTaxDecimal, shippingCostDecimal, oneYearWarrantyDecimal,
            extrasDecimal, clubMembershipDecimal, tireSaleDecimal, discountDecimal As Decimal


            'Declare variables and convert values from textbox controls to memory
            Dim purchasePriceDecimal As Decimal = Decimal.Parse(purchasePriceTextBox.Text, Globalization.NumberStyles.Currency)
            Dim quantityPurchasedInteger As Integer = Integer.Parse(quantityPurchasedTextBox.Text, Globalization.NumberStyles.Number)

            If customerNameTextBox.Text = String.Empty Then
                MessageBox.Show("Customer name cannot be blank", "Customer name error",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)
                customerNameTextBox.Focus()
            End If

            If shippingAddressTextBox.Text = String.Empty Then
                MessageBox.Show("Shipping address cannot be blank", "Shipping address error",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)
                customerNameTextBox.Focus()
            End If

            If telephoneMaskedTextBox.Text = String.Empty Then
                MessageBox.Show("Phone number cannot be blank", "Telephone error",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)
                customerNameTextBox.Focus()
            End If
            'Determine the shipping cost if fed ex air is clicked
            If fedExAirRadioButton.Enabled Then
                shippingCostDecimal = FED_EX_AIR
            ElseIf fedExGroundRadioButton.Enabled Then
                shippingCostDecimal = FED_EX_GROUND
            ElseIf USPostalRadioButton.Enabled Then
                shippingCostDecimal = US_POSTAL
            End If

            'Calculate total shipping cost
            shippingCostDecimal *= quantityPurchasedInteger

            'Show the results in a textbox
            shippingCostTextBox.Text = shippingCostDecimal

            'Check extras
            If oneYearWarrantyCheckBox.Checked Then
                oneYearWarrantyDecimal = ONE_YEAR_WARRANTY
            End If
            If clubMembershipCheckBox.Checked Then
                clubMembershipDecimal = CLUB_MEMBERSHIP
            End If
            If tireSaleCheckBox.Checked Then
                tireSaleDecimal = TIRE_SALE
            End If

            'Determine extrasDecimal
            extrasDecimal = oneYearWarrantyDecimal + clubMembershipDecimal + tireSaleDecimal

            'Determine the discount
            If wholesaleRadioButton.Checked Then
                discountDecimal = (purchasePriceDecimal * quantityPurchasedInteger) * WHOLESALE_DISCOUNT

            ElseIf retailRadioButton.Checked Then
                discountDecimal = RETAIL_DISCOUNT
            End If

            subtotalDecimal = purchasePriceDecimal * quantityPurchasedInteger + shippingCostDecimal + extrasDecimal - discountDecimal

            'Determine the sales tax
            If wholesaleRadioButton.Checked Then
                salesTaxDecimal = 0.0
            ElseIf retailRadioButton.Checked Then
                salesTaxDecimal = subtotalDecimal * SALES_TAX
            End If

            'Determine the total due
            totalDueDecimal = subtotalDecimal + salesTaxDecimal


            'Display output in textboxes
            salesTaxTextBox.Text = salesTaxDecimal.ToString("C")
            subtotalTextBox.Text = subtotalDecimal.ToString("C")
            shippingCostTextBox.Text = shippingCostDecimal.ToString("C")
            costOfExtrasTextBox.Text = extrasDecimal.ToString("C")
            discountTextBox.Text = discountDecimal.ToString("C")
            totalDueTextBox.Text = totalDueDecimal.ToString("C")


            'Enable\Disable buttons
            computeButton.Enabled = False
            resetButton.Enabled = True

            'Accumulate totals
            totalDiscountDecimal += discountDecimal
            totalQuantityInteger += quantityPurchasedInteger

        Catch ex As Exception
            MessageBox.Show("Product identifier, purchase price, or quantity purchased has not been entered!",
                            "Customer name error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

    End Sub

    Private Sub totalCountAverageButton_Click(sender As Object, e As EventArgs) Handles totalCountAverageButton.Click
        'Try statement to check for errors
        Try
            'Determine the average Discount
            Dim averageDiscountDecimal = totalDiscountDecimal / totalQuantityInteger

            'Display totals in a message string
            Dim messageString As String = "Total Wholesale Discounts: " & totalDiscountDecimal.ToString("C") &
                                        ControlChars.NewLine & "Total Wholesale Quantity Sold: " & totalQuantityInteger.ToString("N0") &
                                        ControlChars.NewLine & "Average Discount Amount: " & averageDiscountDecimal.ToString("C")

            'Display a header for the message string
            MessageBox.Show(messageString, "Totals, Counts and Averages", MessageBoxButtons.OK, MessageBoxIcon.Information)

        Catch exArithmeticException As ArithmeticException
            MessageBox.Show("No products have been sold yet", "Zero Sales Message", MessageBoxButtons.OK, MessageBoxIcon.Information)

        Catch ex As Exception
            MessageBox.Show("Unexpected error - inform the system administrator", "Unknown error in totals",
                            MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try
    End Sub

    Private Sub resetButton_Click(sender As Object, e As EventArgs) Handles resetButton.Click
        'Clear the textboxes
        customerNameTextBox.Clear()
        shippingAddressTextBox.Clear()
        telephoneMaskedTextBox.Clear()
        productIdentifierTextBox.Clear()
        purchasePriceTextBox.Clear()
        quantityPurchasedTextBox.Clear()
        shippingCostTextBox.Clear()
        costOfExtrasTextBox.Clear()
        discountTextBox.Clear()
        subtotalTextBox.Clear()
        salesTaxTextBox.Clear()
        totalDueTextBox.Clear()

        'Set radio buttons back to default
        wholesaleRadioButton.Checked = True
        fedExAirRadioButton.Checked = True

        'Uncheck all the extras checkboxes
        oneYearWarrantyCheckBox.Checked = False
        clubMembershipCheckBox.Checked = False
        tireSaleCheckBox.Checked = False

        'Set the focus to the customer name textbox
        customerNameTextBox.Focus()

        'Enable\disable buttons
        computeButton.Enabled = True
        resetButton.Enabled = False
    End Sub

    Private Sub exitButton_Click(sender As Object, e As EventArgs) Handles exitButton.Click
        'Exit the program with being prompted to exit
        Dim response As Integer
        response = MessageBox.Show("Do you want to close the form?", "Quit?", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2)

        If response = vbYes Then
            Me.Close()
        End If
    End Sub

End Class

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Print out the values as the error occurs.

Code:

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Catch ex As Exception
            MessageBox.Show("Product identifier, purchase price, or quantity purchased has not been entered!",
            ' Debug.Print        x & vbCrLf & y  & vbCrLf & z

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It should help identify the error. You can use an ON ERROR statement, with the TRY/CATCH

Doesn't look quite like classic VB6 to me. is this .net you're working with by any chance?

I used your advice and added a messagebox to check each textbox and worked great with the exception of the masked textbox. I am guessing since there are '(', ')', and '-' already in the textbox that I will need to use a different way of checking to make sure all 10 digits are entered. All i found was the following code which did not work

If telephoneTextbox.Text = nothing then

Here is the code which I have shortened up....

Code:

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          'Declare Dim statements to check for errors
            Dim customerNameError As New System.Text.StringBuilder
            Dim shippingAddressNameError As New System.Text.StringBuilder
            Dim telephoneError As New System.Text.StringBuilder
            Dim productIdentifierError As New System.Text.StringBuilder

            'If statement to check if customer name is blank
            If String.IsNullOrWhiteSpace(customerNameTextBox.Text) Then
                customerNameError.AppendLine("Name required")
                customerNameTextBox.Focus()
            End If

            'Message box for error in customer name
            If customerNameError.ToString.Length > 0 Then
                MessageBox.Show(customerNameError.ToString, "Error in Customer Information", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Exit Sub
            End If

            'If statement to check if shipping address is blank
            If String.IsNullOrWhiteSpace(shippingAddressTextBox.Text) Then
                shippingAddressNameError.AppendLine("Shipping address required")
                shippingAddressTextBox.Focus()
            End If

            'Message box for error in shipping address
            If shippingAddressNameError.ToString.Length > 0 Then
                MessageBox.Show(shippingAddressNameError.ToString, "Error in Shipping Information", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Exit Sub
            End If

            'If statement to check if telephone number is valid
            If String.IsNullOrWhiteSpace(telephoneMaskedTextBox.Text) Then
                telephoneError.AppendLine("Telephone required")
            End If

            'Message box for error in telephone number
            If telephoneError.ToString.Length < 0 Then
                MessageBox.Show(customerNameError.ToString, "Error in Telephone Number", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Exit Sub
            End If

            'If statement to check if product identifier is blank
            If String.IsNullOrWhiteSpace(productIdentifierTextBox.Text) Then
                productIdentifierError.AppendLine("Product Identifier required")
                productIdentifierTextBox.Focus()
            End If

            'Messagebox for error in product identifier
            If productIdentifierError.ToString.Length < 0 Then
                MessageBox.Show(productIdentifierError.ToString, "Errors in Purchase Information", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Exit Sub
            End If

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Use a HIDDEN textbox for the MASKED TB. Let user type into normal textbox, check it, and then show the MTB with the value