how to send grid row data after the multiple selection

protected void Button1_Click(object sender, EventArgs e)
    {


        // StringBuilder object
        StringBuilder str = new StringBuilder();


        // Select the checkboxes from the GridView control
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            GridViewRow row = GridView1.Rows[i];
            bool isChecked = ((CheckBox)row.FindControl("chkSelect")).Checked;


            if (isChecked)
            {
                // Column 2 is the Hoarding_ID column
                //str.Append(GridView1.Rows[i].Cells[2].Text);          


                string a = row.Cells[2].Text;
                Session["a"] = a.ToString();
            //} removed from here






            //if (isChecked)
            //{
                //string a = row.Cells[2].Text;
                //Session["a"] = a.ToString();
            //}




        con.Open();
        SqlDataAdapter da = new SqlDataAdapter("select email_id from Hoarding_buyers where username = '" + Session["b"].ToString() + "'", con);
        DataSet ds = new DataSet();
        da.Fill(ds);
        DataTable dt = ds.Tables[0];
        con.Close();


        if (Session["b"] != null)
        {


            System.Web.Mail.MailMessage objMM = new System.Web.Mail.MailMessage();
            objMM.To = dt.Rows[0][0].ToString();
            objMM.From = "[email protected]";


            objMM.BodyFormat = System.Web.Mail.MailFormat.Text;
            objMM.Priority = System.Web.Mail.MailPriority.High;
            objMM.Subject = "HoardingIndia";
            objMM.Body = "Dear Sir/Madam,\r\n\r\n" +
                         "Thank You for Contacting Us. \r\n" +
                         "Our Marketing Team will contact you soon.\r\n\r\n" +
                         "Thanks & regards \r\n" +
                         "Hoardingindia.co.in \r\n" +
                         "011-22239165, +91-8826225511 \r\n\r\n";


            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserver"] = "smtp.gmail.com";
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"] = 465;
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendusing"] = 2;
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpauthenticate"] = 1;
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendusername"] = "hoardingindia2012";
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/sendpassword"] = "hoardingindia2012";
            objMM.Fields["http://schemas.microsoft.com/cdo/configuration/smtpusessl"] = true;
            System.Web.Mail.SmtpMail.SmtpServer = "smtp.gmail.com";
            System.Web.Mail.SmtpMail.Send(objMM);


            con.Open();
            SqlDataAdapter da1 = new SqlDataAdapter("select * from Hoarding_buyers where username = '" + Session["b"].ToString() + "'", con);
            DataSet ds1 = new DataSet();
            da1.Fill(ds1);
            DataTable dt1 = ds1.Tables[0];
            con.Close();


            con.Open();
            SqlDataAdapter da2 = new SqlDataAdapter("select * from providers_post where h_id = '" + Session["a"].ToString() + "'", con);
            DataSet ds2 = new DataSet();
            da2.Fill(ds2);
            DataTable dt2 = ds2.Tables[0];
            con.Close();


            con.Open();
            SqlDataAdapter da3 = new SqlDataAdapter("select * from providers where provider_user_name in (select Provider_user_name from providers_post where h_id = '" + Session["a"].ToString() + "')", con);
            DataSet ds3 = new DataSet();
            da3.Fill(ds3);
            DataTable dt3 = ds3.Tables[0];
            con.Close();




            System.Web.Mail.MailMessage objMM1 = new System.Web.Mail.MailMessage();
            objMM1.To = "[email protected]";
            objMM1.From = "[email protected]";


            objMM1.BodyFormat = System.Web.Mail.MailFormat.Text;
            objMM1.Priority = System.Web.Mail.MailPriority.High;
            objMM1.Subject = "HoardingIndia";
            objMM1.Body = "Dear Sir/Madam,\r\n\r\n" +


          "We have received the details from hoarding buyer. \r\n\r\n" +


                "Name        :" + dt1.Rows[0][1].ToString() + "\r\n" +
                "Email        :" + dt1.Rows[0][10].ToString() + "\r\n" +
               "Contact No.:" + dt1.Rows[0][3].ToString() + "\r\n\r\n" +


          "-----------------------------------------------------------------------" + "\r\n\r\n" +


          "Following are the hoarding details. \r\n\r\n" +


                "Hoarding ID:" + Session["a"].ToString() + "\r\n\r\n" +
                "Address     :" + dt2.Rows[0][1].ToString() + "\r\n" +
                "LandMark :" + dt2.Rows[0][6].ToString() + "\r\n" +
                "State        :" + dt2.Rows[0][4].ToString() + "\r\n" +
                "District     :" + dt2.Rows[0][5].ToString() + "\r\n" +
                "Pin Code  :" + dt2.Rows[0][8].ToString() + "\r\n" +
                "Size         :" + dt2.Rows[0][3].ToString() + "\r\n" +
                "From Date:" + dt2.Rows[0][9].ToString() + "\r\n" +
                "To Date    :" + dt2.Rows[0][14].ToString() + "\r\n\r\n" +
               "Hoarding Type:" + dt2.Rows[0][11].ToString() + "\r\n" +
               "Lighting Type :" + dt2.Rows[0][15].ToString() + "\r\n" +
               "Hoarding Cost:" + dt2.Rows[0][7].ToString() + "\r\n\r\n" +






           "-----------------------------------------------------------------------" + "\r\n\r\n" +


           "Following are the Hoarding owner's details in which buyer is intereated: \r\n\r\n" +


                "Name         :" + dt3.Rows[0][1].ToString() + "\r\n" +
                "Email Id      :" + dt3.Rows[0][6].ToString() + "\r\n" +
              "Contact No.: " + dt3.Rows[0][2].ToString() + "\r\n\r\n\r\n";


            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserver"] = "smtp.gmail.com";
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"] = 465;
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendusing"] = 2;
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpauthenticate"] = 1;
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendusername"] = "hoardingindia2012";
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/sendpassword"] = "hoardingindia2012";
            objMM1.Fields["http://schemas.microsoft.com/cdo/configuration/smtpusessl"] = true;
            System.Web.Mail.SmtpMail.SmtpServer = "smtp.gmail.com";
            System.Web.Mail.SmtpMail.Send(objMM1);


            //Response.Write("");
            //Response.Redirect("search.aspx");
        }// added here

        }
        }
        // prints out the result
        Response.Write(str.ToString());
    }