maths function!!!!!!!!

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maths function!!!!!!!!

I am new to vb, as you will see below.

I am constructing a simple form which requires some basic maths, whem I try to multiply, the compliers states "C:\Documents and Settings\Jones\My Documents\Visual Studio Projects\VB EXAMPLES\stock2\frmorder.vb(168): Operator '*' is not defined for types 'System.Windows.Forms.TextBox' and 'System.Windows.Forms.TextBox'."

What do I need to set to get the cmdcalc_click function to work. It will not handle the multiplication char


Private Sub cmdcalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdcalc.Click

txttotalprice = txtprice * txtqty

End Sub

Cheers, Jason

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maths function!!!!!!!!

  • Pete Farmer

    Daniel,

    Thanks for your help.

    I have tried this solution but I get a microsoft development message saying "An unhandled exception of type 'System.InvalidCastException' occurred in microsoft.visualbasic.dll

    Additional information: Cast from string "" to type 'Integer' is not valid.

    Any ideas

    Thanks, Jason

  • fburns

    You first need to get the string that the user entered into the textbox. And because you can do math with text, only numbers, you have to convert it to a number:



    Dim Price As Double = CDbl(txtPrice.Text)
    Dim Quantity As Integer = CInt(txtQty.Text)
    Dim Result As Double = Price * Quantity
    txtTotalPrice.Text = Result.ToString()

     


  • Jeff FR

    Johan,

    Thanks, it worked fine.

    I appreciate your observations, I come from an industrial background (robotics and plc control) so I am just finding my feet in .net

    Cheers, Jason

  • World Piece

    Observation 1:

    You are trying to multiply two textboxes with each other, not the text in the textboxes. Try this instead:



    txttotalprice.Text = txtprice.Text * txtqty.Text

     


    Observation 2:
    Personally, I don't like to allow the compiler to make all of these magic conversions - I'm an "Option Strict On" type of guy. While it can be convenient to let the compiler determine that it can actually convert the value of the text in the textboxes into numerical values, multiply those values, and to top it all, convert the resulting numerical values back to a string, I have found it to be a source of hard-to-discover bugs. So you would have to explicitly tell the compiler what types you want to convert the strings to:

    (at the top of the file)


    Option Strict On

     




    TextBox1.Text = (CDbl(TextBox1.Text) * CDbl(TextBox1.Text)).ToString()

     


    Observation 3:
    There is no error handling here. What if the user was nasty enough to put something that wasn't a numerical value in the textbox Or a value that was too big (Yeah, I know, this is somewhat beyond the scope of the original question)

    Best regards,
    Johan Stenberg



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