online exam previous button

Question

in online examination system i am using a previous button and i want that at first question the previous button should hide i am using this code but this is not working tell me where i am wrong

string cs = WebConfigurationManager.ConnectionStrings["LocalSqlServer"].ConnectionString;

        SqlConnection cn = new SqlConnection(cs);

        cn.Open();

        DropDownList2.SelectedIndex = 0;        

        SqlDataAdapter da3 = new SqlDataAdapter("select * from reasoning_en", cn);

        da3.Fill(ds2, "reasoning_en");

        i = Convert.ToInt32(ViewState["i"]) - 1;

        SqlDataAdapter da = new SqlDataAdapter("select * from reasoning_en", cn);

        da.Fill(ds, "reasoning_en");

        ViewState["i"] = (int)ViewState["i"] - 1;

        if (ds != null && (int)ViewState["i"] < ds.Tables[0].Rows.Count)

        {

            q0.Text = ds.Tables[0].Rows[i]["quesno"].ToString();

            ques.Text = ds.Tables[0].Rows[i]["ques"].ToString();

            ans1.Text = ds.Tables[0].Rows[i]["ans1"].ToString();

            ans2.Text = ds.Tables[0].Rows[i]["ans2"].ToString();

            ans3.Text = ds.Tables[0].Rows[i]["ans3"].ToString();

            ans4.Text = ds.Tables[0].Rows[i]["ans4"].ToString();

            ans.Text = ds.Tables[0].Rows[i]["ans5"].ToString();

            String s = "select quesimg from reasoning_en where quesno='" + q0.Text + "'";

            SqlCommand cmd = new SqlCommand(s, cn);

            String path = Server.MapPath("~\\images\\");

            SqlDataReader dr;

            dr = cmd.ExecuteReader();

            dr.Read();

            Image1.Visible = true;//image control will now be visible.

            Image1.ImageUrl = dr["quesimg"].ToString();//stores the image url to corresponding image contol and here Image1 is the id of the image control used

            cn.Close();