class Book
    {
        // Book variables
        string title, subtitle, author;
        int id, part, pages;

        // Adds a new book to the memory stack
        public Book(int id, string title, string subtitle, string author, int part, int pages)
        {
            this.id = id;
            this.title = title;
            this.subtitle = subtitle;
            this.author = author;
            this.part = part;
            this.pages = pages;
        }

        public string Title { get => title; set => title = value; }
        public string Subtitle { get => subtitle; set => subtitle = value; }
        public string Author { get => author; set => author = value; }
        public int Id { get => id; set => id = value; }
        public int Part { get => part; set => part = value; }
        public int Pages { get => pages; set => pages = value; }

        // Object > XML
        public void Book_Add(string path)
        {
            if (File.Exists(path))
            {
                XElement root = XElement.Load(path);
                root.Add(
                    new XElement("book",
                        new XElement("id", id),
                        new XElement("title", title),
                        new XElement("subtitle", subtitle),
                        new XElement("author", author),
                        new XElement("part", part),
                        new XElement("pages", pages)
                    )
                );
                root.Save(path);
            }

            else
            {
                XDocument catalogus = new XDocument(
                new XDeclaration("1.0", "UTF-8", null),
                new XElement("books",
                    new XElement("book",
                        new XElement("id", id),
                        new XElement("title", title),
                        new XElement("subtitle", subtitle),
                        new XElement("author", author),
                        new XElement("part", part),
                        new XElement("pages", pages)
                    )
                )
            );
                catalogus.Save(path);
            }
        }
    }