C# da While ile Çarpma Yapma

c#

        private void button1_Click(object sender, EventArgs e)

        {

            int a, b, c=1;

            a = Convert.ToInt32(textBox1.Text);

            b = Convert.ToInt32(textBox2.Text);

            while (a<=b)

            {

                c = c * a;

                a++;

            }

            label4.Text = c.ToString();

        }