Class Form1
    Dim myobj As Object, answer As Integer
    Sub start() Handles Button1.Click 'this sub executes when the button is clicked.

        myobj = New calcu
        myobj.num1 = 4
        myobj.num2 = 3
        'Should give us 7
        answer = myobj.add()
        If Not answer Then
            MsgBox("Incorrect data type! " & answer)
            'Exit sub to stop the execution of the normal message box
            Exit Sub
        End If

        MsgBox(answer)

    End Sub

End Class

Class calcu
    Public num1 As Integer
    Public num2 As Integer
    Public Function add() As Integer
        If Not IsNumeric(Me.num1) Or Not IsNumeric(Me.num2) Then ' The user entered an invalid char. Return false
            Return False
        End If
        Return Me.num1 + Me.num1 'add the two passed parameters and return the answer
    End Function
End Class