how to write code for next button in online examination and also for previous button

Question table colums are question_id,teacher_id,teacher_question,teacher_answer

namespace project_master
{
    public partial class acnj : System.Web.UI.Page
    {
              
        SqlCommand cmd = new SqlCommand();
        public static int i = 0;
          DataTable dt = new DataTable();
        DataRow drr;
        SqlConnection con = new SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=swatidb;Integrated Security=True;Pooling=False");
         public void Page_Load(object sender, EventArgs e)
        {
            con.Open();
            string s1 = "select student_id from Student where user_name='" + Session["sid"] + "'";
            SqlCommand cmd = new SqlCommand(s1, con);
            SqlDataReader dr;
            dr = cmd.ExecuteReader();
            if (dr.Read())
            {
                Label4_stu_id.Text =dr[0].ToString();//for displaying student_id
                dr.Close();
            }
            SqlDataAdapter da = new SqlDataAdapter("select * from Question where question_id>=1 and question_id<=3", con);
            da.Fill(dt);
            drr = dt.Rows[i];
 
            Label2_tea_que.Text = "Write question below in Textbox  click next to get questoion";
           // i++;
        }
         public void next_Click(object sender, System.EventArgs e)
         {
             if (i == (dt.Rows.Count - 1))
             {
                 Response.Write("Last record !");
             }
             else
             {
                 i++;
             }

             Label3_que_id.Text = Convert.ToString(drr[0]);//this label for displaying question_id
             Label2_tea_que.Text = Convert.ToString(drr[2]); //this label for displaying Teacher question
          }
       }   
    }