a gridview row databound value change

in agridview row databound if aquantity value 2.when we add a new row the previous quantity valuealso return 1 .but i want this textbox value assign with previous value 2.plz give the solution.here i have written code.

if (e.Row.RowType == DataControlRowType.DataRow)

{

int i = 1;

TextBox t = (TextBox)e.Row.FindControl("txtquantity");

t.Text = Convert.ToString(i);

Session["quantity"] = t.Text;

txttotalitem.Text = t.Text;

Session["quantity"] = GridView1.Rows.Count;

i want only row which added newly his value will 1 but previous row value means old row value remain unchanged.