VB 08 Calculator

[jac130]

i have to make a calculator in visual basic, it's slightly more complex one, using a combo box/procedures/functions. Anyway, i need to create a user defined function to make sure both input numbers (of the the calculation) are in fact numbers, the isnumeric function. both numbers have to be checked in the same function, and i must return a msgbox (as part of the function) displaying an error and return a value indicating there was a problem. it always crashes when i test it - entering a letter instead of a number into either of the textboxes. here's my code so far: the first function is the function that's malfunctioning. any help would be great

Public Class Form1
 
    Function checknumber(ByVal num1 As String, ByVal num2 As String) As Boolean
        If Not IsNumeric(num1) Then
            MsgBox("Input must be a number.")
        ElseIf Not IsNumeric(num2) Then
            MsgBox("Input must be a number.")
            Return False
        End If
    End Function
 
    Private Sub btnEquals_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEquals.Click
        Dim num1, num2 As Double
        num1 = CStr(txtNum1.Text)
        num2 = CStr(txtNum2.Text)
 
        If cmbOperation.Text = "Addition" Then
            checknumber(num1, num2)
            'calculate result
            addition(num1, num2)
        End If
 
        If cmbOperation.Text = "Subtraction" Then
            'calculate result
            subtraction(num1, num2)
        End If
 
        If cmbOperation.Text = "Multiplication" Then
            'calculate result
            multiplication(num1, num2)
        End If
 
        If cmbOperation.Text = "Division" Then
            'calculate result
            division(num1, num2)
        End If
 
        If cmbOperation.Text = "Mod" Then
            'calculate result
            modular(num1, num2)
        End If
        If cmbOperation.Text = "Exponentiation" Then
            'calculate result
            exponentiate(num1, num2)
        End If
 
        'validate operation 
        If cmbOperation.Text = "" Then
            MsgBox("no operation is selected.")
        End If
    End Sub
 
 
    Sub addition(ByVal num1 As Double, ByVal num2 As Double)
        checknumber(num1, num2)
        txtResult.Text = (num1 + num2)
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
 
    Sub subtraction(ByVal num1 As Double, ByVal num2 As Double)
        txtResult.Text = num1 - num2
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
 
    Sub multiplication(ByVal num1 As Double, ByVal num2 As Double)
        txtResult.Text = num1 * num2
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
 
    Sub division(ByVal num1 As Double, ByVal num2 As Integer)
        'validate input
        If num2 = 0 Then
            MsgBox("Number 2 cannot be 0.")
            Exit Sub
        End If
        txtResult.Text = num1 / num2
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
    Sub modular(ByVal num1 As Double, ByVal num2 As Double)
        'validate input
        If num2 = 0 Then
            MsgBox("Number 2 cannot be 0.")
            Exit Sub
        End If
        txtResult.Text = num1 Mod num2
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
    Sub exponentiate(ByVal num1 As Double, ByVal num2 As Double)
        'validate input
        If num1 = 0 And num2 < 0 Then
            MsgBox("input is invalid.")
            Exit Sub
        End If
        txtResult.Text = num1 ^ num2
        'build list
        lstResults.Items.Add(txtResult.Text)
    End Sub
    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
        lstResults.Items.Clear()
        txtNum1.Text = ""
        txtNum2.Text = ""
        txtRound.Text = ""
        txtResult.Text = ""
        cmbOperation.Text = ""
        radRound.Checked = False
    End Sub
 
    Private Sub radRound_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles radRound.CheckedChanged
        'disable rounding option unless user wants to round
        If radRound.Checked = True Then
            'allow user to round
            txtRound.Enabled = True
        Else
            'do not allow rounding
            txtRound.Enabled = False
        End If
    End Sub
 
    Private Sub lstResults_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstResults.SelectedIndexChanged
        If lstResults.SelectedIndex >= 0 Then
            If MsgBox("Use this number in the calculation?", MsgBoxStyle.YesNo) = MsgBoxResult.Yes Then
                txtNum1.Text = lstResults.Text
            End If
        End If
        If lstResults.SelectedIndex = -1 Then
            MsgBox("no number is selected.")
            Exit Sub
        End If
    End Sub
End Class

[NeoPa]

Homework Assignment

The experts on this site are more than happy to help you with your problems but they cannot do your assignment/program for you. Attempt the assignment/program yourself first and post questions regarding any difficulties you have or about a particular function of the code that you don't know how to achieve.

Administrator.

[NeoPa]

I have also moved this to the appropriate forum for VB questions. You posted it in the Access / VBA forum.

[jac130]

Homework Assignment

The experts on this site are more than happy to help you with your problems but they cannot do your assignment/program for you. Attempt the assignment/program yourself first and post questions regarding any difficulties you have or about a particular function of the code that you don't know how to achieve.

Administrator.

i did attempt it myself, where do you think all that code came from. i only asked about the user defined function validating the input as a number.

[NeoPa]

I have no argument with what you say, as far as it goes.

If you read my post carefully though (in your position I would have) you will see that it also mentions posting questions regarding any difficulties that you may have come across. All your question stated was that your function wasn't working. There is nowhere any description of the difficulties you encountered. What you attempted to do to resolve your initially observed problem.

As a student (of whatever form) we are not prepared to help sabotage your learning process by allowing you (or anyone in your position) simply to drop their problem on the forum and expect solutions to be provided. If you read our rules in the readily available Help link, you will see why we take this stance with students particularly.

We are more than willing to help, but for you we would rather help you to learn, than simply do it for you.

Now, I am happy to help you with this (as I've already become involved) although I am a VBA man more than VB. I don't imagine this will be too much of a block though. At this level they are very similar I understand. I would expect you to start with explaining exactly what goes wrong, and what, if anything, are your thoughts on why this is happening.

Alternatively you can wait for a more specialist VB expert to help. Either way, you should know we would expect you to drive. We would only be there to give guidance.

[jac130]

the rest of the calculator works, but when i type a letter into either of the textboxes and try to calculate it, the program crashes. I have no idea why this happens. the code looks fine to me. i need it to validate that the inputs are numbers but it just crahses.

[NeoPa]

Function checknumber(ByVal num1 As String, ByVal num2 As String) As Boolean
  If Not IsNumeric(num1) Then
    MsgBox("Input must be a number.")
  ElseIf Not IsNumeric(num2) Then
    MsgBox("Input must be a number.")
    Return False
  End If
End Function

Ok, What sort of crash is it. I'm assuming degree level here - is that right?
A shool pupil can possibly get away with just "it crashes."

I need to know WHERE it crashes and what the error message was if there was one. Describe clearly what happens or I can't help you.

PS. I asssume this code has compiled successfully.

[jg007]

can you merge the two threads here please.

** Admin edit - Spoonfeeding help removed **

[NeoPa]

Sorry to cut your help out there JG. We have to be careful how we handle homework type questions though, and simply feeding answers is not acceptable (although I very much sympathise with - and applaud - your wanting to help).

I have locked the other thread (need help with VB 08 Calculator) you referred to, as explained in that thread.

[NeoPa]

I should add that you are, of course, free to offer further assistance, but with the proviso that you extract the solution from the OP themselves, rather than provide it for them.

Possibly direct them where to look, but don't give out answers directly. This doesn't help them (or anyone really) in the long run.

[NeoPa]

I've just been told that, as this is in VB 08, it must be a .NET question rather than a VB one.

I am moving it to the .NET forum.