private void zeroButton_Click(object sender, RoutedEventArgs e)
 {
     part1 = Convert.ToDouble(ScreenText.Text);
     ScreenText.AppendText("" + zero);
 }
 private void nineButton_Click(object sender, RoutedEventArgs e)
 {
     ScreenText.AppendText("" + nine);
 }
 private void eightButton_Click(object sender, RoutedEventArgs e)
 {
     ScreenText.AppendText("" + eight);
 }
 private void sevenButton_Click(object sender, RoutedEventArgs e)
 {
     ScreenText.AppendText("" + seven);
 }
 private void fourButton_Click(object sender, RoutedEventArgs e)
 {
     ScreenText.AppendText("" + four);
 }
 private void TwoButton_Click(object sender, RoutedEventArgs e)
 {
     ScreenText.AppendText("" + two);
 }