求两个日期之间的天数

 private void Form1_Load(object sender, EventArgs e)
        {
            this.textBox1.Text = "2008-10-15";
            this.textBox2.Text = "2008-10-25";
        }

        private void button1_Click(object sender, EventArgs e)
        {
            DateTime t1 = Convert.ToDateTime(textBox1.Text);
            DateTime t2 = Convert.ToDateTime(textBox2.Text);

            TimeSpan ts = t2 - t1;
            int d = ts.Days;
            textBox3.Text = d.ToString();

        }