"Conversion from string "" to type 'Double' is not valid"

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Hey i'm very new to VB and have been attempting a question that requires me to display "fail" in the statusbox when two or more scores have a value less than 5, it seems to work for txtbox1 and txtbox2 but if i try any other textboxes then it comes up with an error.

"Conversion from string "" to type 'Double' is not valid"

i know this is real basic stuff but it's got me stuck

thanks in advance!

VB

If Not IsNumeric(TxtboxS1.Text & TxtboxS2.Text & TxtboxS3.Text) Then
    MessageBox.Show("Data not valid")
End If

If TxtboxS1.Text < 5 And (TxtboxS2.Text < 5) Then
    LblStatusBox.Text = "Fail"

ElseIf TxtboxS1.Text < 5 And (TxtboxS3.Text < 5) Then
    LblStatusBox.Text = "Fail"

ElseIf TxtboxS2.Text < 5 And (TxtboxS3.Text < 5) Then
    LblStatusBox.Text = "Fail"

Else : LblStatusBox.Text = "Pass"

End If

Posted 22-Mar-15 1:51am

doastdot

Updated 22-Mar-15 2:03am

Tomas Takac

v2

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OriginalGriff · Accepted Answer · 2015-03-22T02:06:00

Look at your code:

VB

If Not IsNumeric(TxtboxS1.Text & TxtboxS2.Text & TxtboxS3.Text) Then
   MessageBox.Show("Data not valid")
End If

But you then continue as if it was all ok - so if I enter "Hello" in textbox 51 you will show me a message to say that's bad - and then continue to crash anyway!

Instead, use TryParse to convert the values:

VB

Dim s1 As Double, s2 As Double, s3__1 As Double
If Not (Double.TryParse(txtBoxS1.Text, s1) AndAlso Double.TryParse(txtBoxS2.Text, s2) AndAlso Double.TryParse(txtBoxS3.Text, s3__1)) Then
    MessageBox.Show("Data not valid")
Else
    If s1 < 5 AndAlso s2 < 5 Then
        LblStatusBox.Text = "Fail"
    ElseIf s1 < 5 AndAlso S3 < 5 Then
        ...
End If

phil.o · Accepted Answer · 2015-03-22T02:09:00

That does not work like you did. You have to do the test for each and every textbox. Moreover, the logical AND operator in VB is AndAlso; but I think you need an OR operator here (OrElse in VB):

VB

If Not IsNumeric(Txtbox51.Text) OrElse Not IsNumeric(Txtbox52.Text) OrElse Not IsNumeric(Txtbox53.Text)
   ''
End If

This can be also expressed with an AND operator this way:

VB

If Not (IsNumeric(Txtbox51.Text) AndAlso IsNumeric(Txtbox52.Text) AndAlso IsNumeric(Txtbox53.Text))
   ''
EndIf

There remains to parse the text to double values; OriginalGriff explained that to you in Solution 1.

CPallini · Accepted Answer · 2015-03-22T02:15:00

For each of your TextBoxes you should validate data this way:

VB

Dim score As Long
If Long.TryParse(txbFirst.Text, score) Then
  If score < 5 Then
    LblStatusBox.Text = "Fail"
  End If
Else
  MessageBox.Show("Data not valid")
End If

Of course you'd better define just a Function to perform such validation and pass it the TextBoxes text iteratively (consider using an array of controls).

"Conversion from string "" to type 'Double' is not valid"

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"Conversion from string "" to type 'Double' is not valid"

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