foreach DataListItem for

    protected void txtKarsilanan_TextChanged(object sender, EventArgs e)
    {
        for (int i = 0; i < DataList1.Items.Count; i++)
        {

            foreach (DataListItem k in DataList1.Items)
            {

                Label lblID = (Label)k.FindControl("lblID");
                TextBox txtTE = (TextBox)k.FindControl("txtKarsilanan");

                con.Open();

                SqlDataAdapter adp = new SqlDataAdapter("UPDATE Siparisler SET TedarikEdilen='" + txtTE.Text + "' WHERE CartID='" + lblID.Text + "'", con);
                DataTable dt = new DataTable();

                adp.Fill(dt);
                con.Close(); 
                adp.Dispose();
                dt.Clear();

            }
        }

        Response.Redirect("GelenSiparisler.aspx");
    }