Visual Studio按钮代码错误

Question

This is my first time using visual studio and I'm running into an error with my tax calulator application. The problem is that visual studio is saying that the multiplication line using "*" and "+" can not be done due to the variables being text boxes. So my question to the community, is should I change the text box to something else? Or where in my code did I mess up.

Public Class Form1
    Private Sub btnCalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
        If (IsNumeric(txtSale) And IsNumeric(txtSalesTaxRate)) Then
            lblTax = txtSale * txtSalesTaxRate
            lblTotal = txtSale + lblTax
        Else
            MsgBox("Please enter valid numbers, thank you!")
        End If

    End Sub
End Class

If you need me to give you the full layout of my application, do ask.

Answer 1

I can see multiple problems in your code. I will explain how the "vs" works.The textboxes that you've made are controls.
You can't just take their value so simple.They have many property and one of them is .text which allows you to take the value inside them.
Another mistake you've made is what you've tried to do with the textboxes.What you type in those textboxes is ..well text. The program can't tell if the value inside is a number or just text. You must convert that value in a number using Cint.
So you're code will look like this:

Public Class Form1
Private Sub btnCalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
    If (IsNumeric(txtSale.text) And IsNumeric(txtSalesTaxRate.text)) Then
        lblTax.text= cint(txtSale.text) * cint(txtSalesTaxRate.text)
        lblTotal.text= cint(txtSale.text) + cint(lblTax.text)
    Else
        MsgBox("Please enter valid numbers, thank you!")
    End If

End Sub
End Class

What cint does is to convert every type of data to integer. Also the .text property lets you to set the value of the control (in our case the label caption)

Answer 2

I tried Electric-web's code and ran into a problem with the output. I changed "CInt" to "CDbl" and the tax calculator worked.

    Public Class Form1
Private Sub btnCalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
    If (IsNumeric(txtSale.text) And IsNumeric(txtSalesTaxRate.text)) Then
        lblTax.text= cdbl(txtSale.text) * cdbl(txtSalesTaxRate.text)
        lblTotal.text= cdbl(txtSale.text) + cdbl(lblTax.text)
    Else
        MsgBox("Please enter valid numbers, thank you!")
    End If

End Sub
End Class