DataRow dr = table1.NewRow();
          //1是把所有列进行汇总
           //for (int i = 1; i < table1.Columns.Count; i++)
           // {
               // dr = table1.Compute("Sum(" + table1.Columns.ColumnName + ")", "true");   
            //}


           //仅对需要的列进行汇总
             decimal xxx = 0;
            decimal xxx1 = 0;
             for (int i = 1; i < table1.Rows.Count; i++)
             {
                 
                 xxx  += Convert.ToDecimal(table1.Rows["衣服用费"]);
                 dr[1]=xxx;
                 
                 xxx1 += Convert.ToDecimal(table1.Rows["住宿费用"]);
                 dr[2] = xxx1;

            }

            table1.Rows.Add(dr);

            GridView1.DataSource = table1;