private void TextBoxEquation_TextChanging(TextBox sender, TextBoxTextChangingEventArgs args)
{
    try
    {
        int selectionIndex = textBoxEquation.SelectionStart;
        string simpleNum = textBoxEquation.Text.Replace(",", "");
        var value = string.Format("{0:N0}", long.Parse(simpleNum));
        textBoxEquation.Text = value;
        textBoxEquation.SelectionStart = selectionIndex + 1;
    }
    catch { }
}