How to store last button clicked and add to listbox

Question

So I'm doing this calculator program and need the numbers, the operator used and the "=" sign to show up in the listbox so "1 + 1 = 2" should show up. I have the calculator working and can move items to the listbox, but can't figure out how to remember the button that was clicked to get the outcome and move it over also.

Option Explicit On
Option Strict On
Option Infer Off

Public Class Form1

Private Sub ButtonAdd_Click(sender As Object, e As EventArgs) Handles ButtonAdd.Click     
    Result.Text = CStr(Val(NumOne.Text) + Val(NumTwo.Text))
End Sub

Private Sub ButtonSub_Click(sender As Object, e As EventArgs) Handles ButtonSub.Click
    Result.Text = CStr(Val(NumOne.Text) - Val(NumTwo.Text))
End Sub

Private Sub ButtonMul_Click(sender As Object, e As EventArgs) Handles ButtonMul.Click
    Result.Text = CStr(Val(NumOne.Text) * Val(NumTwo.Text))
End Sub

Private Sub ButtonDiv_Click(sender As Object, e As EventArgs) Handles ButtonDiv.Click
    Result.Text = CStr(Val(NumOne.Text) / Val(NumTwo.Text))
    'outputs a message box telling the user to correct the division by 0, also displays a blank result box instead of NaN
    If CDbl(NumTwo.Text) = Val(0) Then
        Result.Text = ""
        MessageBox.Show("You cannot divide by 0, please input another number")
    End If

End Sub

Private Sub ButtonExit_Click(sender As Object, e As EventArgs) Handles ButtonExit.Click
    Me.Close()
End Sub

Private Sub ButtonSave_Click(sender As Object, e As EventArgs) Handles ButtonSave.Click
    ListBox1.Items.Add(NumOne.Text & NumTwo.Text & Result.Text)
End Sub

End Class

Answer 1

As far as you just need to store one character, you can rely on the Tag property of ListBox1 (basically, a black box where you can store anything you want). Sample code:

Private Sub ButtonAdd_Click(sender As Object, e As EventArgs) Handles ButtonAdd.Click     
    Result.Text = CStr(Val(NumOne.Text) + Val(NumTwo.Text))
    ListBox1.Tag = "+"
End Sub

Private Sub ButtonSub_Click(sender As Object, e As EventArgs) Handles ButtonSub.Click
    Result.Text = CStr(Val(NumOne.Text) - Val(NumTwo.Text))
    ListBox1.Tag = "-"
End Sub

Private Sub ButtonMul_Click(sender As Object, e As EventArgs) Handles ButtonMul.Click
    Result.Text = CStr(Val(NumOne.Text) * Val(NumTwo.Text))
    ListBox1.Tag = "x"
End Sub

Private Sub ButtonDiv_Click(sender As Object, e As EventArgs) Handles ButtonDiv.Click
    Result.Text = CStr(Val(NumOne.Text) / Val(NumTwo.Text))
    'outputs a message box telling the user to correct the division by 0, also displays a blank result box instead of NaN
    If CDbl(NumTwo.Text) = Val(0) Then
        Result.Text = ""
        MessageBox.Show("You cannot divide by 0, please input another number")
    End If
    ListBox1.Tag = "/"
End Sub

Private Sub ButtonExit_Click(sender As Object, e As EventArgs) Handles ButtonExit.Click
    Me.Close()
End Sub

Private Sub ButtonSave_Click(sender As Object, e As EventArgs) Handles ButtonSave.Click
    ListBox1.Items.Add(NumOne.Text & ListBox1.Tag.ToString() & NumTwo.Text & "=" & Result.Text)
End Sub