input digits, float numbers and negative numbers in TextBox

private void txtDigitsWithDotsAndMinus_KeyPress(object sender, KeyPressEventArgs e)
{
    TextBox txt = (TextBox)sender;
    int pos = txt.SelectionStart;

    //ввод точки (запятой)
    if ((txt.Text.StartsWith(".")) || (txt.Text.StartsWith(",")))
    {
        // добавление лидирующего ноля
        txt.Text = "0" + txt.Text;
        txt.SelectionStart = pos + 1;
    }

    if ((e.KeyChar == '.') || (e.KeyChar == ','))
    {
        if (txt.Text.Contains(".") || txt.Text.Contains(","))
        {
            e.Handled = true;
            return;
        }

        return;
    }

    //ввод минуса
    if (e.KeyChar == '-')
    {
        if (txt.Text.StartsWith("-"))
        {
            txt.Text = txt.Text.Substring(1);
            txt.SelectionStart = pos - 1;
        }
        else
        {
            txt.Text = "-" + txt.Text;
            txt.SelectionStart = pos + 1;
        }

        e.Handled = true;
        return;
    }

    //ввод цифр
    if (!(Char.IsDigit(e.KeyChar)))
    {
        if ((e.KeyChar != (char)Keys.Back))
        {
            e.Handled = true;
        }
    }
}