Multiple Check box in Grid view in Asp.Net with C#

-----check Box code in Gridview(only selected check Box)-----------


if (GridView1.Rows.Count > 0)
        {
            for (int i = 0; i < GridView1.Rows.Count; i++)
            {

                CheckBox chk1 = (CheckBox)GridView1.Rows[i].Cells[4].FindControl("chk");
                   
                string id = GridView1.Rows[i].Cells[0].Text;
                string count=GridView1.Rows[i].Cells[1].Text;
                int step=Convert.ToInt32(GridView1.Rows[i].Cells[2].Text);
                string reward=GridView1.Rows[i].Cells[3].Text;
                if (chk1.Checked == true)
                {
                    //con.update_data("update Payout set Flag='Y',cheque=0 where MainID='" + id + "'");
                    string main = con.select_data_scalar_string("select MainID from EndUserLevel where UserID='" + id + "'");
                    string date=DateTime.Now.ToString();
                    con.insert_data("insert into tbl_Reward values('"+main+"','"+id+"','"+reward+"',"+step+",'"+date+"')");
                    RMG.Functions.MsgBox("Data Has Been inserted Successfully");
                    MultiView1.ActiveViewIndex = 1;
                }
            }
        }



-----Check Box code in Gridview(for all rows of gridview)-----

  string[] StoreID = new string[GridView1.Rows.Count];

        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            CheckBox chk1 = (CheckBox)GridView1.Rows[i].Cells[6].FindControl("chk");
            if (chk1.Checked == true)
            {
                StoreID[i] = StoreID[i] + GridView1.Rows[i].Cells[0].Text;
                con.update_data("Update tbl_Withdrawl Set flag=1 Where MainID='" + StoreID[i].ToString() + "' ");              

            }
            RMG.Functions.MsgBox("Successfully Confirumed");
        }

----use of Datakey in Gridview(datakey use for pass the values(using queryString ) of gridview to another page;)-----


 protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "Page")
        {
            GridView1.PageIndex = Int32.Parse((string)(e.CommandArgument)) - 1;

        }
        else
        {
            GridView _gridView = (GridView)sender;

            // Get the selected index and the command name
            int _selectedIndex = int.Parse(e.CommandArgument.ToString());
            string _commandName = e.CommandName;
            string MainID = "",  BinaryIncome = "", ClubIncome = "", UniversalIncome = "", RefferalIncome = "",Reward = "", TDS = "", Ccharge = "", Net_Amount = "", cheque = "", Date1 = "";
           
           
            MainID = GridView1.DataKeys[_selectedIndex].Values["MainID"].ToString();


            BinaryIncome = GridView1.DataKeys[_selectedIndex].Values["tbl_BinaryIncome"].ToString();
            ClubIncome = GridView1.DataKeys[_selectedIndex].Values["Club_Income"].ToString();
            UniversalIncome = GridView1.DataKeys[_selectedIndex].Values["tbl_UniversalIncome"].ToString();
            RefferalIncome = GridView1.DataKeys[_selectedIndex].Values["tbl_RefferalIncome"].ToString();
            Reward = GridView1.DataKeys[_selectedIndex].Values["tbl_Reward"].ToString();          
            TDS = GridView1.DataKeys[_selectedIndex].Values["TDS"].ToString();
            Ccharge = GridView1.DataKeys[_selectedIndex].Values["ccharge"].ToString();
            Net_Amount = GridView1.DataKeys[_selectedIndex].Values["Amount"].ToString();
            cheque = GridView1.DataKeys[_selectedIndex].Values["cheque"].ToString();
            //Date = GridView1.DataKeys[_selectedIndex].Values["Date"].ToString();
            Date1 = GridView1.DataKeys[_selectedIndex].Values["cheque_date"].ToString();
            Response.Redirect("Statements.aspx?MainID=" + MainID + "&BinaryIncome=" + BinaryIncome + "&ClubIncome=" + ClubIncome + "&UniversalIncome=" + UniversalIncome + "&RefferalIncome=" + RefferalIncome + "&Reward=" + Reward + "&TDS=" + TDS + "&Ccharge=" + Ccharge + "&Net_Amount=" + Net_Amount + "&cheque=" + cheque + "&Date1=" + Date1);
           
        }
    }



----------checkbox coding (headercheckbox)------


protected void chkheader_CheckedChanged(object sender, EventArgs e)
    {

        checkBind();
    }

private void checkBind()
    {
        if (GridView1.Rows.Count > 0)
        {
            CheckBox chHeader = (CheckBox)GridView1.HeaderRow.Cells[10].FindControl("chkheader");
            if (chHeader.Checked == true)
            {
                for (int i = 0; i < GridView1.Rows.Count; i++)
                {
                    CheckBox chk1 = (CheckBox)GridView1.Rows[i].Cells[11].FindControl("chk");
                    chk1.Checked = true;
                }
            }

            if (chHeader.Checked == false)
            {
                for (int i = 0; i < GridView1.Rows.Count; i++)
                {
                    CheckBox chk1 = (CheckBox)GridView1.Rows[i].Cells[11].FindControl("chk");
                    chk1.Checked = false;
                }
            }
        }
    }