///<summary>
        ///Creates a new invoice entry (InvoiceEntry object ) and add it to the invoice.
        ///It first calculates the new entry’s line number, then use the new line number together with the passed (item) object
        ///and the requested quantity (ReqQuantity) to call the InvoiceEntry Constructor to create the new InvoiceEntry object.
        ///Finally, adds the object to the invoice.  This method must use the passed item object to check the
        ///requested quantity against the item’s available quantity before creating and adding the new entry.
        ///It also must update the item’s available quantity based on the requested quantity if quantity verification is passed.
        ///</summary>
        public bool addInvEntry(Item item, int ReqQuantity)
        {
            invoiceList.Add(item);
            // List<List>.IndexOf() should return 0 based index of the item we are searching for
            // for logical reasons I added 1 so our lineitems don't start at 0:
            // ref: https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.indexof?view=netframework-4.8
            updateTotal(item.UnitPrice);
            InvoiceEntry LineItem = new InvoiceEntry(item, invoiceList.IndexOf(item) + 1, ReqQuantity);

            //check to see if we have enough in inventory,
            float itemInInventory = item.updateAvlblQty(ReqQuantity);

            if (itemInInventory != -1)
            {
                //we have enough in inventory; update the avallable quantity:
                item.avallableQty = item.avallableQty - ReqQuantity;
                //updateTotal(ReqQuantity);
                return(true);
            }
            return(false);
        }
        int total;          // sum of the prices of all items in the invoice (must be updated whenever an item added/removed from the invoice)

        public void newInvoceEntry(InvoiceEntry invoice)
        {
        }