Track last 5 or 10 visited products like shopping ites in as

I prefer lists over arrays, so for the example I use a list. The trick I would use is to store the list in a session variable; cookie might also work, but no experience with them.

namespace WebApplication1
{
    public partial class LastItems : System.Web.UI.Page
    {
        ///

        /// list with IDs of last items
        ///

        List g_lstLastItems;

        protected void Page_Load(object sender, EventArgs e)
        {
            // read lastitems from session
            g_lstLastItems = Session["LastItems"] == null ? new List() : (List)Session["LastItems"];
            if (!IsPostBack)
            {
                // display last items
                displayLastitems();
            }
        }

        protected void btnSubmit_Click(object sender, EventArgs e)
        {
            // make space for new item
            if (g_lstLastItems.Count == 5)
                g_lstLastItems.RemoveAt(0);

            // random number to simulate
            Random rnd = new Random();

            // add 'new' last item to list
            g_lstLastItems.Add(rnd.Next(1, 101));

            // update session variable
            Session["LastItems"] = g_lstLastItems;

            // display result
            displayLastitems();
        }

        ///

        /// display
        ///

        private void displayLastitems()
        {
            tbLastItems.Text = "";
            for (int cnt = 0; cnt < g_lstLastItems.Count; cnt++)
            {
                tbLastItems.Text += String.Format("{0} ", g_lstLastItems[cnt]);
            }
        }

    }
}

g_lstLastItems holds a list of IDs of the last items. When the page is loaded, it is filled with the values stored in the session variable and the last items are displayed

I've used a button click to simulate the user viewing a certain item. The item is identified by a random number (you can use the real IDs of the items).

If a limit is reached (5 items in the example), first make space in the list, next add to the list, update the session variable and display the result in a textbox.

Instead of IDs, you can store strings containing a complete URL for an item or whatever. You can also consider use of a HashSet instead of a List; in that case there will never be a duplicate in the 'list'.