Private Sub btn1_Click(sender As Object, e As EventArgs) Handles btn1.Click
        If cb1.SelectedIndex = 0 Then
            tb3.Text = Int(tb1.Text) + Int(tb2.Text)
        End If

        If cb1.SelectedIndex = 1 Then
            tb3.Text = Int(tb1.Text) - Int(tb2.Text)
        End If

        If cb1.SelectedIndex = 2 Then
            tb3.Text = Int(tb1.Text) / Int(tb2.Text)
        End If

        If cb1.SelectedIndex = 3 Then
            tb3.Text = Int(tb1.Text) * Int(tb2.Text)
        End If

        If cb1.SelectedIndex = 4 Then

        End If

        If cb1.SelectedIndex = 5 Then
            If tb1.Text = "" Then
                tb3.Text = Math.Sin(tb2.Text)
            End If
        Else
            tb3.Text = Math.Sin(tb2.Text) * Int(tb1.Text)
        End If

        If cb1.SelectedIndex = 6 Then
            If tb1.Text = "" Then
                tb3.Text = Math.Cos(tb2.Text)
            End If
        Else
            tb3.Text = Math.Cos(tb2.Text) * Int(tb1.Text)
        End If

        If cb1.SelectedIndex = 7 Then
            If tb1.Text = "" Then
                tb3.Text = Math.Tan(tb2.Text)
            End If
        Else
            tb3.Text = Math.Tan(tb2.Text) * Int(tb1.Text)
        End If

    End Sub
End Class