public Form1() { InitializeComponent(); IEdition book1 = new Directory(1987, 3, "A5", 253, "Hard", "Name1"); IEdition book2 = new Directory(1998, 2, "A4", 61, "Soft", "Name2"); Directory book3 = new Directory(2004, 1, "A4", 521, "Hard", "Name3"); IEdition book4 = new Directory(2013, 4, "A5", 413, "Hard", "Name4"); Directory book5 = new Directory(1977, 3, "A4", 644, "Hard", "Name5"); book1.AddAuthor(2); book4.RemoveAuthor(1); book5.ChangeName("Name55"); book3.SetBinding("Soft"); List <IEdition> Books = new List <IEdition> { book1, book2, book3, book4, book5 }; for (int i = 0; i < Books.Count; i++) { textBox1.Text += Books[i].ToString(); } }