srno value is incremented but when page is refreshed then its value again reset and shows srno=1. how to increment value.

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using System.Data;

namespace CustomRaghav.VisualWebPart1
{
    public partial class VisualWebPart1UserControl : UserControl
    {
        HiddenField HFSN = new HiddenField();
        DataTable table = new DataTable();
        DataTable result = new DataTable();
        private int srno = 1;
        private string headlines;
        private string date;
        Button btn = new Button();

        private const string _ascxPath = @"~/_CONTROLTEMPLATES/GridViewWP/GridView8/VisualWebPart1UserControl.ascx";
        private Microsoft.SharePoint.WebControls.SPGridView _grid;
        protected void Page_Load(object sender, EventArgs e)
        {
        }

        protected override void CreateChildControls()
        {
            table = GetDataTable();
            btn.Visible = true;
            btn.Text = "Show";
            btn.Click += new EventHandler(btn_Click);
            _grid = new Microsoft.SharePoint.WebControls.SPGridView();
            _grid.AutoGenerateColumns = false;
            _grid.AllowPaging = true;
            _grid.PageSize = 5;
            //_grid.PageIndexChanging += _grid_PageIndexChanging;
            foreach (DataColumn column in table.Columns)
                _grid.Columns.Add(new BoundField()
                {
                    DataField = column.ColumnName,
                    HeaderText = column.ColumnName
                });
            //_grid.DataSource = table;
            this.Controls.Add(_grid);
            // _grid.PagerTemplate = null;
            _grid.DataBind();
            _grid.Visible = true;
            this.Controls.Add(btn);
        }


        void btn_Click(object sender, EventArgs e)
        {

            //srno = Convert.ToInt32(HFSN.Value);
            DataRow[] rows = table.Select();
            if (srno <= rows.Length)
            {
                for (int i = 0; i < rows.Length; i++)
                {

                    if (rows[i]["srno"].ToString() == srno.ToString())
                    {

                        headlines = rows[i]["headlines"].ToString();
                        date = rows[i]["date"].ToString();
                    }

                }

                if ((srno) == 1)
                {
                    result.Columns.Add("srno", typeof(int));
                    result.Columns.Add("date", typeof(string));
                    result.Columns.Add("Headlines", typeof(string));
                }
                result.Rows.Add(new object[] { srno, date, headlines });
            }

            srno++;
            //HFSN.Value =Convert.ToString(srno);

            _grid.DataSource = result;
            _grid.DataBind();
            // DataTable table = GetDataTable();

            _grid.Visible = true;


        }



        private DataTable GetDataTable()
        {
            //  DataTable result = new DataTable();

            table.Columns.Add("srno", typeof(int));
            table.Columns.Add("headlines", typeof(string));
            table.Columns.Add("date", typeof(System.DateTime));
            //for (int i = 1; i <= 5; i++)
            table.Rows.Add(new object[] { 1, "Chinese Troops Begin Withdrawing from Ladakh Hours after Xi-Modi meet", "2014-09-22" });
            table.Rows.Add(new object[] { 2, "BJP-Shiv Sena Alliance of 25 years on verge of Collapse", "2014-09-21" });
            table.Rows.Add(new object[] { 3, "Meet THe Highest Female Executive In the World", "2014-09-22" });
            table.Rows.Add(new object[] { 4, "Indian Muslims will Live And Die For India,PM Says", "2014-09-21" });
            table.Rows.Add(new object[] { 5, "Two Doctors, Who got stuck in J&K floods, turn saviours for this town", "2014-09-21" });
            return table;


        }
    }
}