MainWindow.xaml.cs

using Microsoft.CodeAnalysis.CSharp.Scripting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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;

namespace Math
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            this.DataContext = new ViewModel();
        }

        private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (int.TryParse(((TextBox)sender).Text, out int result))
            {
                ((ViewModel)DataContext).OnResultChanged(result);
            }
        }

        private void TextBox_KeyDown(object sender, KeyEventArgs e)
        {
            if(e.Key == Key.Enter)
            {
                ((ViewModel)DataContext).Next();
            }
        }
    }
}