How to Subtract multiple textbox value in c# visual studio.

Subtraction for multiple textbox value in c# 
for example, add three textboxes and one button from the toolbox and then go to the button1 click event and copy the following code.
private void button1_Click(object sender, EventArgs e)
        {

             int a=0;
             int b=0;
             int c=0;

            if (int.TryParse(textBox1.Text, out a) & int.TryParse(textBox2.Text, out b))
            {
                c = a - b;
                textBox3.Text = c.ToString();
            }
        }