Public Class Frmcalculadora

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub
    Sub efectuo(ByVal operaciones As String)
        Dim num1, num2, resultado As Double
        Dim textomostrar As String
        Dim operok As Boolean
        operok = True

        num1 = numero(Txtnum1.Text)
        num2 = numero(Txtnum2.Text)
        Txtnum1.Text = num1
        Txtnum2.Text = num2
        Select Case operaciones
            Case "+"
                resultado = num1 + num2
            Case "-"
                resultado = num1 - num2
            Case "X"
                resultado = num1 * num2
            Case "/"
                If num2 <> 0 Then
                    resultado = num1 / num2
                Else
                    operok = False
                End If

        End Select
        If operok Then
            Lblresultado.Text = resultado
            textomostrar = num1 & operaciones & num2 & "=" & resultado
            cboresultados.Items.Add(textomostrar)
            lstresultados.Items.Add(textomostrar)


        End If



    End Sub
    Function numero(ByVal valor As String) As Double
        Dim retorno As Double
        If IsNumeric(valor) Then
            retorno = valor
        Else
            retorno = 0
        End If

        Return (retorno)
    End Function
    Private Sub cmdsuma_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdsuma.Click
        efectuo("+")

    End Sub

    Private Sub cmdresta_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdresta.Click
        efectuo("-")
    End Sub

    Private Sub cmdmultiplicacion_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdmultiplicacion.Click
        efectuo("*")

    End Sub

    Private Sub cmddivision_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmddivision.Click
        efectuo("/")
    End Sub
End Class