WPF DataTable rows adding problem

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C#

WPF

DataTable

Need simple help

I have two data table. I have method which copying data columns from dt data table to dtHelper table like this:

foreach (DataColumn col in dt.Columns)
        {
            string colname = col.ColumnName.ToString();
            dtHelper.Columns.Add("" + colname + "", dt.Columns["" + col + ""].DataType);
        }

This method receiving three values int CheckInID,string _ServiceName and _ServicePrice than adding new column which columName is servicename than copying rows from dt to dthelper and adding serviceName column serviceprice where ID = CheckInID

this is how:

ArrayList arr = ConvertDT(ref dt);
           foreach (Object obj in arr)
           {
               string _ID = ((DataRow)obj)["ID"].ToString();
               string _RoomType = ((DataRow)obj)["Room Type"].ToString();
               string _RoomNumber = ((DataRow)obj)["Room"].ToString();
               string _RoomPrice = ((DataRow)obj)["Room Price"].ToString();
               string _Discount = ((DataRow)obj)["Discount"].ToString();
               string _DiscountedPrice = ((DataRow)obj)["Discounted Price"].ToString();
               string _CheckInDate = ((DataRow)obj)["Check In Date"].ToString();
               string _CheckOutDate = ((DataRow)obj)["Check Out Date"].ToString();
               string _TotalDays = ((DataRow)obj)["Total Days"].ToString();
               string _TotalPrice = ((DataRow)obj)["Total Price"].ToString();
               Boolean _IncFirstDay = Convert.ToBoolean(((DataRow)obj)["Inc. First Day"]);
               string _PaidMoney = ((DataRow)obj)["Paid Money"].ToString();

               if (Convert.ToInt32(_ID) == CheckInID)
               {

                   _ServiceName = ServiceName;
                   dtHelper.Rows.Add(
                       _ID,
                       _RoomType,
                       _RoomNumber,
                       _RoomPrice,
                       _Discount,
                       _DiscountedPrice,
                       _CheckInDate,
                       _CheckOutDate,
                       _TotalDays,
                       _TotalPrice,
                       _IncFirstDay,
                       _PaidMoney,
                       _ServicePrice);
               }
               else
               {
                   dtHelper.Rows.Add(
                        _ID,
                        _RoomType,
                        _RoomNumber,
                        _RoomPrice,
                        _Discount,
                        _DiscountedPrice,
                        _CheckInDate,
                        _CheckOutDate,
                        _TotalDays,
                        _TotalPrice,
                        _IncFirstDay,
                        _PaidMoney,
                        _ServicePrice);
               }
               _ServicePrice = "";

So this works very well but the problem is that when I second service it, adding in first servicename column, I don't know in advance how much services would be (user adding it with window).

How can I modify _dtHelper.Rows.Add?

For example if I added service (which name is skis serv) and in table create a new column, then I added price below that column and along for example 25 ID row.

I want to add second service(restaurant service) on ID 27 it would be something like that : enter image description here and it must be like this

http://imageshack.us/photo/my-images/32/2222im.png/[^]

http://imageshack.us/photo/my-images/855/firstal.png/[^]