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Label3.Text = Label1.Text * Label2.Text  -> Input string was not in a correct format

Posted on 2010-09-21
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Last Modified: 2012-05-10
I've been working on this half the day and it's ticking me off.

I've got four text boxes for input.  They are restricted to numeric values only with JavaScript.

Then there are three labels.

Label1 gets its value from TextBox1 * TextBox2
Label2 gets its value from TextBox3 * TextBox4
Label3 gets its valaue from Label1 * Label2

The work is done in the "CalculateButton" click event.

In the last IF/THEN,
If Double.TryParse(lblNumberTrainingHours.Text, 0) Then
is failing, causing tNumber to be zero thus making AmountReimbursed equal zero.

lblNumberTrainingHours.Text contains a correctly calculated value of "140" so I don't know why its failing the Double.TryParse.

This has gotten so convoluted in my efforts to make it calculate those few values and not crash if there are no values to calculate.  It could probably be done more correctly with, like three lines of code.  ;-)
Protected Sub btnRecalculate_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnRecalculate.Click
        Call UpdateTotals()
    End Sub

    Protected Sub UpdateTotals()
        '##################################################################################From txtTrainingPaymentPercent.TextChanged
        Dim Wage, Percent, Rate As Double
        If Double.TryParse(txtTraineeEntryWage.Text, 0) Then
            'Wage = Double.TryParse(txtTraineeEntryWage.Text, 0)
            Wage = CType(txtTraineeEntryWage.Text, Double)
        Else
            Wage = 0
        End If
        If Double.TryParse(txtTrainingPaymentPercent.Text, 0) Then
            'Percent = Double.TryParse(txtTrainingPaymentPercent.Text, 0)
            Percent = CType(txtTrainingPaymentPercent.Text, Double)
        Else
            Percent = 0
        End If

        Rate = Wage * Percent / 100

        lblTrainingPaymentHourlyRate.Text = Rate.ToString ' txtTraineeEntryWage.Text * txtTrainingPaymentPercent.Text / 100

        '##################################################################################From txtHoursPerWeek.TextChanged
        Dim tWeeks, tHours, tRate, tNumber, TrainingHours, AmountReimbursed As Double
        If Double.TryParse(txtLengthTrainingWeeks.Text, 0) Then
            'tWeeks = Double.TryParse(txtLengthTrainingWeeks.Text, 0)
            tWeeks = CType(txtLengthTrainingWeeks.Text, Double)
        Else
            tWeeks = 0
        End If
        If Double.TryParse(txtHoursPerWeek.Text, 0) Then
            'tHours = Double.TryParse(txtHoursPerWeek.Text, 0)
            tHours = CType(txtHoursPerWeek.Text, Double)
        Else
            tHours = 0
        End If
        If Double.TryParse(lblTrainingPaymentHourlyRate.Text, 0) Then
            'tRate = Double.TryParse(lblTrainingPaymentHourlyRate.Text, 0)
            tRate = CType(lblTrainingPaymentHourlyRate.Text, Double)
        Else
            tRate = 0
        End If
        If Double.TryParse(lblNumberTrainingHours.Text, 0) Then
            'tNumber = Double.TryParse(lblNumberTrainingHours.Text, 0)
            tNumber = CType(lblNumberTrainingHours.Text, Double)
        Else
            tNumber = 0
        End If

        TrainingHours = tWeeks * tHours
        AmountReimbursed = tRate * tNumber

        lblNumberTrainingHours.Text = TrainingHours.ToString ' tHours * tWeeks ' txtLengthTrainingWeeks.Text * txtHoursPerWeek.Text
        lblMaxAmountReimbursed.Text = AmountReimbursed.ToString ' tRate * tNumber ' lblTrainingPaymentHourlyRate.Text * lblNumberTrainingHours.Text


    End Sub

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Question by:megnin
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Expert Comment

by:käµfm³d 👽
ID: 33727946
You appear to be using TryParse incorrectly. The second parameter to TryParse is a reference paramter. If TryParse succeeds, then the ref parameter will already have the value as a double stored in it--there is no need to cast it using CType. Here is an example:
Dim value As String = "43.5"
Dim result As Double

If Double.TryParse(value, result) Then
    ' TryParse succeeded and result now is the double value 43.5. No cast required.
End If

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Author Comment

by:megnin
ID: 33727986
Yes, I see.  Just goes to show, just because you "Google" something doesn't mean it's correct.  ;-)
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LVL 75

Expert Comment

by:käµfm³d 👽
ID: 33728038
>>  just because you "Google" something doesn't mean it's correct

That's what EE is for  ;)
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LVL 1

Author Comment

by:megnin
ID: 33728096
I've got it like this now and it works:
If Double.TryParse(txtTraineeEntryWage.Text, Wage) Then
  ' Wage = CType(txtTraineeEntryWage.Text, Double)
Else
Wage = 0
End If
If I just say,
Double.TryParse(txtTraineeEntryWage.Text, Wage)
and the TryParse fails what with the value of Wage be?
Should I do this?
Dim Wage As Double = 0
Then if it fails will it just be "0"?
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Accepted Solution

by:
käµfm³d   👽 earned 500 total points
ID: 33728174
I think this will suit you and clarify:
Dim Wage As Double

If Not Double.TryParse(value, Wage) Then
    ' TryParse failed. Set value equal to zero
    Wage = 0
End If

' If TryParse succeeds, then the "If" is never entered. Because the
'  second param to TryParse is ByRef, Wage will already be set if
'  TryParse succeeds. If TryParse fails, then the "If" is entered
'  and Wage is set to zero

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Author Comment

by:megnin
ID: 33728248
Thank you for the explanation.  That helps.
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Author Closing Comment

by:megnin
ID: 33728261
Thank you for making it easy to understand.
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LVL 75

Expert Comment

by:käµfm³d 👽
ID: 33728605
NP. Glad to help  :)
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