DataTable中添加一列序号

        /// 

        /// 添加一列序号
        /// 
        /// 需要添加序号列的表
        /// DataTabel
        private DataTable AddCol( DataTable dt)
        {
                DataTable dtR;   //返回值
                DataColumn dtNewCol = new DataColumn("Id", typeof(string)); //创建ID列
                dt.Columns.Add(dtNewCol);
                dt.Columns["Id"].SetOrdinal(0);
                dtR= dt;
                int dtc = dtR.Rows.Count;    //dtc  行数
                for (int i = 0; i < dtc; i++)
                {
                    dtE.Rows[i]["Id"] = (i + 1).ToString();
                }
            return dtR;
        }