// variaveis do form


    Dim OP As String

    Dim a, b, resultado, resp, pi As Double


// botao soma, menos, dividir, multiplicacao

Private Sub Btsoma_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btsoma.Click

        a = TxtCalc.Text
        TxtCalc.Text = " "
        OP = "Suma"

    End Sub

    Private Sub Btmenos_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btmenos.Click
        a = TxtCalc.Text
        TxtCalc.Text = " "
        OP = "Menos"
    End Sub

    Private Sub Btdividir_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btdividir.Click
        a = TxtCalc.Text
        TxtCalc.Text = " "
        OP = "Div"
    End Sub

    Private Sub Btmulti_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btmulti.Click
        a = TxtCalc.Text
        TxtCalc.Text = " "
        OP = "Multi"
    End Sub


// botão do igual

 Private Sub Btigual_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btigual.Click

        b = Val(TxtCalc.Text)

        Select Case OP

            Case "Suma"
                resultado = a + b
                TxtCalc.Text = resultado

            Case "Menos"
                resultado = a - b
                TxtCalc.Text = resultado

            Case "Multi"
                resultado = a * b
                TxtCalc.Text = resultado

            Case "Div"
                resultado = a / b
                TxtCalc.Text = resultado

            Case "Elevado"
                resultado = Math.Pow(a, b)
                TxtCalc.Text = resultado

            Case "Porcento"
                resp = b / 100
                resultado = resp * a
                TxtCalc.Text = resultado

        End Select

    End Sub