Problem catching errors

[hollywoood]

Hello everyone!!

I have an assignment to create that wonderful mortgage calculator. I have the code working, but when i try to catch an error (No matter is it is left blank, or a letter is typed in) the program crashes. Not sure what i am doing wrong, but any in site would be great. Thanks everyone!!

Public Class MortCalc

    Private Sub clearForm()
        txtLoan.Text = 200000
        txtInterest.Text = 5.75
        txtYears.Text = 30
        txtTotal.Text = ""
    End Sub


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
        'New Varables
        Dim txtPrincipal As Double
        Dim txtRate As Double
        Dim txtYears As Integer
        Dim amount As Double
        Dim monthlyRate As Double
        Dim years As Integer

        amount = CDbl(Me.txtLoan.Text)
        monthlyRate = CDbl(Me.txtInterest.Text) / 100 'allows interest rate to be entered whole number'
        years = CInt(Me.txtYears.Text)

        If IsNumeric(txtLoan.Text) = False Then
            MsgBox("Please enter a valid loan amount.")
            txtLoan.Clear()
            txtLoan.Focus()
            Exit Sub
        End If

        If IsNumeric(txtInterest.Text) = False Then
            MsgBox("Please enter a valid Interest Rate")
            txtInterest.Clear()
            txtInterest.Focus()
            Exit Sub
        End If

        If IsNumeric(Me.txtYears.Text) = False Then
            MsgBox("Please enter a valid year")
            Me.txtYears.Clear()
            Me.txtYears.Focus()
        End If



        txtPrincipal = FormatCurrency(amount)
        txtRate = FormatCurrency(monthlyRate)
        txtYears = FormatCurrency(years) * 12

        Dim iRate As Double = monthlyRate / 12
        Dim tTotal As Double = txtPrincipal * (iRate / (1 - (1 + iRate) ^ (-txtYears)))
        Me.txtTotal.Text = Format(tTotal, "$#,##0.00")
    End Sub

    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
        clearForm()
    End Sub

    Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
        End
    End Sub
End Class

[ndeniche]

This is because even though you are validating the textboxes' input, you are not stopping the program's progress... what you what to do is separate the FormatCurrency() functions into a separate function, validated by the IsNumer() results. Something like this:

Public Class MortCalc

    Private Sub clearForm()
        txtLoan.Text = 200000
        txtInterest.Text = 5.75
        txtYears.Text = 30
        txtTotal.Text = ""
    End Sub


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
        'New Varables
        Dim txtPrincipal As Double
        Dim txtRate As Double
        Dim txtYears As Integer
        Dim amount As Double
        Dim monthlyRate As Double
        Dim years As Integer

        amount = CDbl(Me.txtLoan.Text)
        monthlyRate = CDbl(Me.txtInterest.Text) / 100 'allows interest rate to be entered whole number'
        years = CInt(Me.txtYears.Text)

        If Not IsNumeric(txtLoan.Text) Then
            MsgBox("Please enter a valid loan amount.")
            txtLoan.Clear()
            txtLoan.Focus()
            Exit Sub
        End If

        If Not IsNumeric(txtInterest.Text) Then
            MsgBox("Please enter a valid Interest Rate")
            txtInterest.Clear()
            txtInterest.Focus()
            Exit Sub
        End If

        If Not IsNumeric(Me.txtYears.Text) Then
            MsgBox("Please enter a valid year")
            Me.txtYears.Clear()
            Me.txtYears.Focus()
        End If


         If IsNumeric(txtLoan.Text) And IsNumeric(txtInterest.Text) And IsNumeric(txtYears.Text) Then
            txtPrincipal = FormatCurrency(amount)
            txtRate = FormatCurrency(monthlyRate)
            txtYears = FormatCurrency(years) * 12
            Dim iRate As Double = monthlyRate / 12
            Dim tTotal As Double = txtPrincipal * (iRate / (1 - (1 + iRate) ^ (-txtYears)))
            Me.txtTotal.Text = Format(tTotal, "$#,##0.00")
         End If
    End Sub

    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
        clearForm()
    End Sub

    Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
        End
    End Sub
End Class