//---------- RunInterface METHOD ---------------------------------------------------------------------------------------------------------------------------------------------

        public void RunInterface()
        {
            string userInput = "";

            bool isFinished = false;

            while (!isFinished)
            {
                MainMenu();

                userInput = Console.ReadLine();

                switch (userInput)
                {
                case "1":     // Case 1.1 - Display Items
                    DisplayItemCategories();
                    DisplayItems(items);
                    break;

                case "2":     // Case 1.2 - Go to order menu

                    bool isDone = false;
                    while (!isDone)
                    {
                        PurchaseMenu();
                        Console.WriteLine();
                        userInput = Console.ReadLine();

                        switch (userInput)
                        {
                        case "1":            // Case 2.1 - Add Money to Balance
                            Console.WriteLine("Please enter deposit amount (must be an integer)");
                            userInput = Console.ReadLine();
                            string addMoneyMessage = items.AddMoney(userInput);
                            Console.WriteLine(addMoneyMessage);

                            break;

                        case "2":                // Case 2.2 - Select Items

                            Console.WriteLine(); //blank line
                            Console.WriteLine("Please enter valid product code");
                            string checkProduct = Console.ReadLine();

                            Console.WriteLine();         //blank line
                            Console.WriteLine("Please enter desired quantity");
                            string strQuantityDesired = Console.ReadLine();

                            int intQuantityDesired = int.Parse(strQuantityDesired);

                            string checkProductMessage = items.PurchaseIndividualItem(checkProduct, intQuantityDesired);
                            Console.WriteLine(checkProductMessage);

                            CateringItem selectedItem = null;

                            foreach (CateringItem item in items.ItemList)
                            {
                                if (item.Code == checkProduct)
                                {
                                    selectedItem = item;         //allows us to get selected item and pass in below
                                    break;
                                }
                            }
                            if (checkProductMessage == "ITEM ADDED TO CART")
                            {
                                items.UpdateBalance(selectedItem, intQuantityDesired);
                            }
                            break;

                        case "3":         // Case 2.3 - Complete Transaction

                            TenderChange();

                            Console.WriteLine("List of purchased items and total cost this transaction:");
                            Console.WriteLine();

                            DisplayPurchasesCategories();

                            string printList = items.PrintPurchases(items.PurchasedItems);
                            Console.WriteLine(printList);
                            Console.WriteLine();         //blank line
                            Console.WriteLine("Total: " + items.TotalCost);

                            Console.WriteLine();         //blank line
                            string checkOut = items.BalanceToZero();
                            Console.WriteLine(checkOut);
                            Console.WriteLine("Press enter to return to main menu");
                            Console.ReadLine();

                            isDone = true;         //ends the while loop

                            break;

                        default:
                            Console.WriteLine("Please make a valid selection");
                            break;
                        }
                        Console.WriteLine();     //blank line
                    }
                    break;

                case "3":
                    isFinished = true;
                    Console.WriteLine("Press Enter To Exit, Enjoy Your Tasty Tasty Food");
                    break;

                default:
                    Console.WriteLine("Please make a valid selection");
                    break;
                }
                Console.WriteLine(); //blank line
            }
        }