please check my code

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["mycon"].ToString());
                string sql = "select DISTINCT id,MAX(enddate) as enddate from table1 group by id";
                SqlCommand cmd = new SqlCommand(sql, con);
                string d1 = DateTime.Now.ToString("dd/m/yyyy");
                DateTime datenow = new DateTime();
                datenow = Convert.ToDateTime(d1);

                DateTime enddate = new DateTime();
                enddate = Convert.ToDateTime(cmd.ExecuteScalar());

                if (DateTime.Compare(datenow, enddate) > 0)
                {

                    string sql1 = "update users set type='Suspended Users' where users.id in(select DISTINCT id from table1 where enddate ='" + enddate + "')";
                    SqlCommand cmd1 = new SqlCommand(sql1, con);
                    cmd1.ExecuteNonQuery();
                    for (int i = 1; i < 5; i++)
                    {
                        int period = 1;
                        string sql2 = "update table3 set period='" + period + "'";
                        SqlCommand cmd2 = new SqlCommand(sql2, con);
                        cmd2.ExecuteNonQuery();
                        period++;
                    }