private void BuyItem(string username, int id)
        {
            User    user;
            Product product;

            try
            {
                product = StregSystem.GetProductByID(id);
                user    = StregSystem.GetUserByUsername(username);

                if (product.Active)
                {
                    try
                    {
                        StregsystemUI.DisplayUserBuysProduct(StregSystem.BuyProduct(user, product));
                    }
                    catch (InsufficientCreditsException)
                    {
                        StregsystemUI.DisplayInsufficientCash(user, product);
                    }
                }
            }
            catch (UserDoesNotExistException)
            {
                StregsystemUI.DisplayUserNotFound(username);
            }
            catch (InvalidProductIdException)
            {
                StregsystemUI.DisplayProductNotFound(id);
            }
        }
        private void BuyMultipleItems(string[] userCommandArr)
        {
            string username  = userCommandArr[0];
            int    amount    = int.Parse(userCommandArr[1]);
            int    productId = int.Parse(userCommandArr[2]);
            List <BuyTransaction> buyTransactions = new List <BuyTransaction>();

            if (amount > 0)
            {
                try
                {
                    User    user    = StregSystem.GetUserByUsername(username);
                    Product product = StregSystem.GetProductByID(productId);

                    if (product.Active)
                    {
                        for (int i = 0; i < amount; i++)
                        {
                            try
                            {
                                buyTransactions.Add(StregSystem.BuyProduct(user, product));
                            }
                            catch (InsufficientCreditsException)
                            {
                                StregsystemUI.DisplayInsufficientCash(user, product);
                            }
                        }
                        StregsystemUI.DisplayUserBuysProducts(buyTransactions);
                    }
                }
                catch (UserDoesNotExistException)
                {
                    StregsystemUI.DisplayUserNotFound(username);
                }
                catch (InvalidProductIdException)
                {
                    StregsystemUI.DisplayProductNotFound(productId);
                }
            }
            else
            {
                StregsystemUI.DisplayGeneralError("You have to buy atleast one item :)");
            }
        }