gistfile1.cs

void UpdateQuality()
        {
            for (var i = 0; i < Items.Count; i++)
            {
                if (Items[i].Name != "Aged Brie" && Items[i].Name != "Backstage passes to a TAFKAL80ETC concert")
                {
                    if (Items[i].Quality > 0)
                    {
                        if (Items[i].Name != "Sulfuras, Hand of Ragnaros")
                        {
                            Items[i].Quality = Items[i].Quality - 1;
                        }
                    }
                }
                else
                {
                    if (Items[i].Quality < 50)
                    {
                        Items[i].Quality = Items[i].Quality + 1;

                        if (Items[i].Name == "Backstage passes to a TAFKAL80ETC concert")
                        {
                            if (Items[i].SellIn < 11)
                            {
                                if (Items[i].Quality < 50)
                                {
                                    Items[i].Quality = Items[i].Quality + 1;
                                }
                            }

                            if (Items[i].SellIn < 6)
                            {
                                if (Items[i].Quality < 50)
                                {
                                    Items[i].Quality = Items[i].Quality + 1;
                                }
                            }
                        }
                    }
                }

                if (Items[i].Name != "Sulfuras, Hand of Ragnaros")
                {
                    Items[i].SellIn = Items[i].SellIn - 1;
                }

                if (Items[i].SellIn < 0)
                {
                    if (Items[i].Name != "Aged Brie")
                    {
                        if (Items[i].Name != "Backstage passes to a TAFKAL80ETC concert")
                        {
                            if (Items[i].Quality > 0)
                            {
                                if (Items[i].Name != "Sulfuras, Hand of Ragnaros")
                                {
                                    Items[i].Quality = Items[i].Quality - 1;
                                }
                            }
                        }
                        else
                       {
                            Items[i].Quality = Items[i].Quality - Items[i].Quality;
                        }
                    }
                    else
                    {
                        if (Items[i].Quality < 50)
                       {
                            Items[i].Quality = Items[i].Quality + 1;
                        }
                    }
                }
            }
        }

        IList<Item> Items = new List<Item>
            {
                new Item { Name = "+5 Dexterity Vest", SellIn = 10, Quality = 20 },
                new Item { Name = "Aged Brie", SellIn = 2, Quality = 0 },
                new Item { Name = "Elixir of the Mongoose", SellIn = 5, Quality = 7 },
                new Item { Name = "Sulfuras, Hand of Ragnaros", SellIn = 0, Quality = 80 },
                new Item { Name = "Backstage passes to a TAFKAL80ETC concert", SellIn = 15, Quality = 20 },
                new Item { Name = "Conjured Mana Cake", SellIn = 3, Quality = 6 }
            };

        class Item
        {
            public string Name { get; set; }

            public int SellIn { get; set; }

            public int Quality { get; set; }
        }