private void Button_percent_Click(object sender, RoutedEventArgs e)
{
if (operation.containSign(Text_current_operation.Text) == true)
{
Text_result.Text = operation.Result(Text_current_operation.Text).ToString();
Text_current_operation.Text = Text_result.Text + "%";
}
else
{
Text_current_operation.Text += "%";
}
}