سه رقم جدا کردن اعداد در سی شارپ

if (textBox1.Text != string.Empty)
            {
                textBox1.Text = string.Format("{0:N0}", double.Parse(textBox1.Text.Replace(",", "")));
                textBox1.Select(textBox1.TextLength, 0);
            }

private void dedsec(object sender)
        {
            TextBox tb =  (TextBox)sender ;
            if (tb.Text != string.Empty)
            {
                tb.Text = string.Format("{0:N0}", double.Parse(tb.Text.Replace(",", "")));
                tb.Select(tb.TextLength, 0);
            }
        }

dedsec(sender);

public TextBox sender { get; set; }
internal void dedsec(object sender)
        {
            TextBox tb = (TextBox)sender;
            if (tb.Text != string.Empty)
            {
                tb.Text = string.Format("{0:N0}", double.Parse(tb.Text.Replace(",", "")));
                tb.Select(tb.TextLength, 0);
            }
        }

cd.dedsec(sender);

formname cd = new formname();