Invalid Cast Excepton

[outinnowhere]

I get this Error Message and I am lost as to how to fix it. Can someone please help? My code is--

 Dim a, b, r, h As Double
    Dim v As Double
    Const Pi As Double = 3.14
 
 'Assign text box values to variables
        a = CDbl(CStr(CDbl(TextBox1.Text)))
        b = CDbl(CStr(CDbl(TextBox2.Text)))
        r = CDbl(CStr(CDbl(TextBox3.Text)))
        h = CDbl(CStr(CDbl(TextBox4.Text)))
        'Determine checked button and calculate
        Try
            If RadioButton1.Checked = True Then
 
            End If
            v = CDbl(CStr(Sqrt(CDbl(a) ^ 2) + (CDbl(b) ^ 2)))
            TextBox5.Text = CStr(v)
 
        Catch When Err.Number = 6 'if Overflow
            MsgBox("Overflow")
        Catch When Err.Number = 11 'if Division by Zero
            MsgBox("Zero Error")
        Catch When Err.Number = 13 'if typing error
            MsgBox("Typing Error")
        End Try
 
 
        'Uses formula to calculate volume of a cylinder
        Try
            If RadioButton2.Checked = True Then
 
            End If
            v = CDbl(CStr((CDbl(r) * CDbl(r)) * 3.14 * CDbl(h)))
            TextBox5.Text = CStr(v)
        Catch When Err.Number = 6 'if Overflow
            MsgBox("Overflow")
        Catch When Err.Number = 11 'if Division by Zero
            MsgBox("Zero Error")
        Catch When Err.Number = 13 'if typing error
            MsgBox("Typing Error")
 

PLEASE HELP

[Frinavale]

You may be getting this error if the TextBoxes contains Nothing...I just glanced at your code though so I'm not sure.

Which line is the error occurring on?

-Frinny

[debasisdas]

the culprit is the very first line.

in your code only the variable h is double.remaining 3 are variant by default.