public static class DataCart
    {
        private static DataTable myDataTable;
        public static DataTable MyDataTable
        {
            get
            {
                if (myDataTable == null)
                {
                    myDataTable = new DataTable();

                    DataColumn dataTableColumnNum = new DataColumn();
                    DataColumn dataTableColumnId = new DataColumn();
                    DataColumn dataTableColumnName = new DataColumn();
                    DataColumn dataTableColumnCost = new DataColumn();
                    DataColumn dataTableColumnAmount = new DataColumn();

                    dataTableColumnNum.DataType = typeof(Int32);
                    dataTableColumnNum.ColumnName = "№";
                    DataCart.MyDataTable.Columns.Add(dataTableColumnNum);

                    dataTableColumnId.DataType = typeof(Int32);
                    dataTableColumnId.ColumnName = "#";
                    DataCart.MyDataTable.Columns.Add(dataTableColumnId);

                    dataTableColumnName.DataType = typeof(string);
                    dataTableColumnName.ColumnName = "Наименование";
                    DataCart.MyDataTable.Columns.Add(dataTableColumnName);

                    dataTableColumnAmount.DataType = typeof(Int32);
                    dataTableColumnAmount.ColumnName = "Количество";
                    DataCart.MyDataTable.Columns.Add(dataTableColumnAmount);

                    dataTableColumnCost.DataType = typeof(double);
                    dataTableColumnCost.ColumnName = "Цена";
                    DataCart.MyDataTable.Columns.Add(dataTableColumnCost);
                }
                return myDataTable;
            }
        }
    }