{help} basic calculator in visual basic 2008

Hello. I am new to visual basic 2008, and i started with simple project-calculator. I made it to the point where "+" sign works, and "=" sign execute the command of "+" sign. Now i try to make "-" sign work: the problem is, idk how to bind it with "=". Here is the code:

 Public Class Form1
    Dim total1 As Integer
    Dim total2 As Integer
 
    Private Sub btnOne_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOne.Click
        txtDisplay.Text = txtDisplay.Text & btnOne.Text
    End Sub

    Private Sub btnTwo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTwo.Click
        txtDisplay.Text = txtDisplay.Text & btnTwo.Text
    End Sub

    Private Sub btnThree_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnThree.Click
        txtDisplay.Text = txtDisplay.Text & btnThree.Text
    End Sub

    Private Sub btnFour_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFour.Click
        txtDisplay.Text = txtDisplay.Text & btnFour.Text
    End Sub

    Private Sub btnFive_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFive.Click
        txtDisplay.Text = txtDisplay.Text & btnFive.Text
    End Sub

    Private Sub btnSix_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSix.Click
        txtDisplay.Text = txtDisplay.Text & btnSix.Text
    End Sub

    Private Sub btnSeven_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSeven.Click
        txtDisplay.Text = txtDisplay.Text & btnSeven.Text
    End Sub

    Private Sub btnEight_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEight.Click
        txtDisplay.Text = txtDisplay.Text & btnEight.Text
    End Sub

    Private Sub btnNine_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNine.Click
        txtDisplay.Text = txtDisplay.Text & btnNine.Text
    End Sub

    Private Sub btnZero_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnZero.Click
        txtDisplay.Text = txtDisplay.Text & btnZero.Text
    End Sub

    Private Sub cmdPlus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPlus.Click
        total1 = total1 + Val(txtDisplay.Text)
        txtDisplay.Clear()
    End Sub

    Private Sub cmdEquals_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdEquals.Click
        total2 = total1 + Val(txtDisplay.Text)
        txtDisplay.Text = total2
        total1 = 0

    End Sub

    Private Sub cmdClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdClear.Click
        txtDisplay.Clear()
    End Sub

   
    Private Sub cmdMinus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdMinus.Click
        total1 = total1 - Val(txtDisplay.Text)
        txtDisplay.Clear()
    End Sub
End Class

Question is:
how can i use "if" (conditional) statement in this code:

 Private Sub cmdEquals_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdEquals.Click
        total2 = total1 + Val(txtDisplay.Text)
        txtDisplay.Text = total2
        total1 = 0

And do i need to add another value like:

 Dim total3 As Integer

and use it as a "-" button:

 Private Sub cmdMinus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdMinus.Click
        total3 = total3 - Val(txtDisplay.Text)
        txtDisplay.Clear()
    End Sub

????
Please Help.

Thank you.