<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Button Content="Add" Height="23" HorizontalAlignment="Left" Margin="12,78,0,0" Name="button1" VerticalAlignment="Top" Width="120" Click="button1_Click" />
<TextBox Height="23" HorizontalAlignment="Left" Margin="12,12,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" />
<TextBox Height="23" HorizontalAlignment="Left" Margin="12,41,0,0" Name="textBox2" VerticalAlignment="Top" Width="120" />
</Grid>
</Window>
private void button1_Click(object sender, RoutedEventArgs e)
{
MessageBox.Show(Convert.ToString(Convert.ToDouble(textBox1.Text) + Convert.ToDouble(textBox2.Text)), "Addition", MessageBoxButton.OK, MessageBoxImage.Information);
}