find average of variables - vb.net

Question

Full disclosure, I'm working on an assignment for COP2170, but the additional feature isn't apart of the assignment just trying to stretch a little further...
I'm trying to add 5 test scores and output the average of the 5 scores, that part works just fine. In addition I'm trying to add an additional feature that will allow the user to enter less than 5 scores and the program will still output the average of whatever scores were entered.
So this works:
And this works:
The problem I'm running into is if the first score is omitted and the rest are filled in, it doesn't work:
Here's the code I've got so far:
Public Class frmTestScoreAverage
Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click
Dim decScore1, decScore2, decScore3, decScore4, decScore5 As Double ' decScore1-5 to hold test scores1-5
Dim decScoreAverage As Double ' to hold test score average
Dim intDivideBy As Double = 5 ' declare intDivideBy variable with starting value of 5
lblStatusLabel.Text = String.Empty 'set error message to empty string
Try
' Read user input convert to double and assign value to variable
decScore1 = Convert.ToDouble(txtScore1.Text)
decScore2 = Convert.ToDouble(txtScore2.Text)
decScore3 = Convert.ToDouble(txtScore3.Text)
decScore4 = Convert.ToDouble(txtScore4.Text)
decScore5 = Convert.ToDouble(txtScore5.Text)
' Calculate average
decScoreAverage = (decScore1 + decScore2 + decScore3 + decScore4 + decScore5) / intDivideBy
'display result
lblResult.Text = CStr(decScoreAverage)
Catch
' Display error message, asks for all scores
lblStatusLabel.Text = "Please enter all test scores"
'Calculate average even without all scores
For Each c As TextBox In Me.Controls.OfType(Of TextBox)() 'loop through each textbox in form see: http://stackoverflow.com/a/13504361/1947286
If c.Text = String.Empty Then intDivideBy -= 1 'If text equals empty string, Then decrement intDivideBy
Next
'catch divide by zero error
Try
'calculate average
decScoreAverage = (decScore1 + decScore2 + decScore3 + decScore4 + decScore5) / intDivideBy 'add test scores and divide to find average
'display result
lblResult.Text = CStr(decScoreAverage)
Catch
lblStatusLabel.Text = "Please enter at least one test score"
End Try
End Try
End Sub
End Class
I'm pretty sure the problem has to do with the way I'm finding the average:
decScoreAverage = (decScore1 + decScore2 + decScore3 + decScore4 + decScore5) / intDivideBy
Is there a way to find the average that will allow for empty variables in any arrangement?

Answer 1

The problem you are having is that Convert.ToDouble(txtBox.text) (with empty string, will make Convert throw an Exception.
Add a validation that the string isn't empty or use TryParse to see if the Textbox value is parseable to a number.
Either
If not String.IsNullOrEmpty(txtBox.Text) then
Convert.ToDouble(txtBox.text)
Or
dim value as Double
if Double.TryParse(txtBox.Text, value) then
avg += value
When the first one is empty, it goes to the Catch part of the code, then you try to calculate the avg, but the values of the Txtbox are not assigned to the declarations you made, so when it tries to do the average
decScore1 = Convert.ToDouble(txtScore1.Text) // Exception here to Catch
decScore2 = Convert.ToDouble(txtScore2.Text) // Not evaluated
decScore3 = Convert.ToDouble(txtScore3.Text) // Not evaluated
decScore4 = Convert.ToDouble(txtScore4.Text) // Not evaluated
decScore5 = Convert.ToDouble(txtScore5.Text) // Not evaluated
Theses do not have any value, in return this doesn't do what you want
decScoreAverage = (decScore1 + decScore2 + decScore3 + decScore4 + decScore5) / intDivideBy
UPDATE
(Vb code not tested)
Function GetTextValue(dim score as string) as Double
dim value as Double = 0
if (Double.TryParse(score, value))
return value
else
return value
End Function
This
decScore1 = Convert.ToDouble(txtScore1.Text)
Becomes
decScore1 = GetTextValue(txtScore1.Text)

Answer 2

I suggest you store reference to each textbox in an array. You'll see why at the end of this example.
Public Class frmTestScoreAverage
Public Sub New()
Me.InitializeComponent()
Me.boxes = {Me.txtScore1, Me.txtScore2, Me.txtScore3, Me.txtScore4, Me.txtScore5}
End Sub
Private boxes As TextBox()
The common way to validate user input in winforms is to handle the Validating event, usually combined with the error provider class as mentioned by Hans Passant.
Private Sub HandleScoreValidating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles txtScore1.Validating, txtScore2.Validating, txtScore3.Validating, txtScore4.Validating, txtScore5.Validating
With DirectCast(sender, TextBox)
If ((Not String.IsNullOrEmpty(.Text)) AndAlso (Not Double.TryParse(.Text, 0.0R))) Then
e.Cancel = True
'Alert or set error provider:
'Me.ErrorProvider1.SetError(DirectCast(sender, Control), "Not double")
Else
e.Cancel = False
'Clear error provider:
'Me.ErrorProvider1.Clear()
End If
End With
End Sub
Now, back to the textbox array. Create a new list of double and iterate the textbox array. If the text isn't empty, parse and add the value to the list. At the end, use the Average extension method to get the average value.
Private Sub HandleCalculate(sender As Object, e As EventArgs) Handles btnCalculate.Click
Dim values As New List(Of Double)
For Each box As TextBox In Me.boxes
If (Not String.IsNullOrEmpty(box.Text)) Then
values.Add(Double.Parse(box.Text))
'Else
' values.Add(0.0R)
End If
Next
Dim average As Double = values.Average()
'....
End Sub
End Class