เกี่ยวกับวนลูป event.. อธิบายไม่ถูกช่วยดูหน่อยครับ

public static int i = 1;
        public TextBox[] txtRun_Quan, txtRun_Price, txtRun_Amout;
        public Form1()
        {
            InitializeComponent();
        }
        
        protected void Add_Controls()
        {
            i++;
            txtRun_Quan = new TextBox[20];
            txtRun_Price = new TextBox[20];
            txtRun_Amout = new TextBox[20];

            txtRun_Quan[i] = new TextBox();
            txtRun_Price[i] = new TextBox();
            txtRun_Amout[i] = new TextBox();

            txtRun_Quan[i].Text = i.ToString();
            txtRun_Quan[i].Name = "txtRun_Quan" + i;
            txtRun_Price[i].Name = "txtRun_Price" + i;
            txtRun_Amout[i].Name = "txtRun_Amout" + i;

            txtRun_Quan[i].Top = ((txtRun_Quan[i].Height + 5) * i);

            txtRun_Price[i].Left = ((txtRun_Price[i].Width + 5));
            txtRun_Price[i].Top = ((txtRun_Price[i].Height + 5) * i);

            txtRun_Amout[i].Left = ((txtRun_Price[i].Left +  txtRun_Amout[i].Width + 5));
            txtRun_Amout[i].Top = ((txtRun_Amout[i].Height + 5) * i);

            this.Controls.Add(txtRun_Quan[i]);
            this.Controls.Add(txtRun_Price[i]);
            this.Controls.Add(txtRun_Amout[i]);

            this.txtRun_Price[i].TextChanged += new EventHandler(CalAmouti);
        }

        private void CalAmouti(object sender, EventArgs e)
        {
            for (int i_in = 2; i_in <= i; i_in++)
            {
                if ((txtRun_Price[i_in].Text != "") && (txtRun_Quan[i_in].Text != ""))
                {
                    txtRun_Amout[i_in].Text = Convert.ToString(Convert.ToInt16(txtRun_Price[i_in].Text) * Convert.ToInt16(txtRun_Quan[i_in].Text));
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Add_Controls();
        }