static int LinearSearch(item[] array, int target)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i].quantity == target)
                {
                    return i;
                }
            }
            return -1;
        }

        static int LinearSearch(item[] array, int target)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i].quantity == target)
                {
                    return i;
                }
            }
            return -1;
        }