In Gridview Template Field textbox , how to write nexttextbox move in for loop

using System.Configuration;

protected void btnUpdae_Click(object sender, EventArgs e)
{
 string connection = ConfigurationManager.ConnectionStrings["QuestionnaireConnection"].ConnectionString;
  using (SqlConnection con = new SqlConnection(connection))
    {
        con.Open();

       //Button is outside Gridview and no command argument or command name is given 
       //UserProfileDataContext UR = new UserProfileDataContext(); 
       //if (!IsPostBack)  

        //[here the row count is zero 
        if (grdView.Rows.Count > 0)
          {

            //[if I have break point here I am not getting into the loop] 
            foreach (GridViewRow row in grdView.Rows) 
                    {
                        for (int i = 0; i < grdView.Rows.Count; i++)
                        {
                            for (int txtComments = 0; txtComments < grdView.Columns.Count; txtComments++)
                            {
                                
                                Question qs = new Question();
                                string name = Request.QueryString["UserName"];
                                string temp1 = grdView.Rows[i].Cells[0].Text;

                                //string temp2 =(TextBox)grdView.Rows[i].Cells[3].FindControl("txtComments")
                                TextBox t1 = (TextBox)grdView.Rows[i].Cells[3].FindControl("txtComments");

                                string temp2 = t1.Text;
                                //SqlCommand cmd = new SqlCommand("UPDATE Questionnaire_UserAnswers 
                                //SET Comments='" +    
                                //temp2 + "' WHERE Question_ID='" + temp1 + "'", con);
                                //cmd.ExecuteNonQuery();
                                SqlDataAdapter da;
                                da = new SqlDataAdapter("UPDATE Questionnaire_UserAnswers SET Comments='" + temp2 + "'  
                                                        WHERE Question_ID=" + temp1 + "", con);

                                DataSet ds = new DataSet();
                                da.Fill(ds);


                                if (ds.Tables.Count > 0)
                                {
                                    if (ds.Tables[0] != null)
                                    {
                                        grdView.DataSource = ds.Tables[0];
                                        grdView.DataBind();
                                    }
                                }