Ok I am try to make a simple calculator, and it looks like every thing if working find, but my btn.Text isn't is giving me the Error

'System.Windows.Controls.Button' does not contain a definition for 'Text' and no extension method 'Text' accepting a first argument of type 'System.Windows.Controls.Button' could be found (are you missing a using directive or an assembly reference?)

I am not sure what I am supposed to do here.

TBoxMain.Text+= btn.Text;
I am currently using

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Collections;
using System.ComponentModel;

please help,
thanks