static void Main(string[] args) { L1 : Console.WriteLine("choose the number:1 for rectangle, 2 for square and 3 for triangle"); int choice = Convert.ToInt32(Console.ReadLine()); switch (choice) { case 1: Console.WriteLine("enter the length and width in order:"); Rectangle shape1 = new Rectangle(Convert.ToDouble(Console.ReadLine()), Convert.ToDouble(Console.ReadLine())); if (shape1.legal()) { Console.WriteLine("legal" + "\n and the area is " + shape1.area_calculating()); } else { Console.WriteLine("illegal" + "\n therefore, the area can not be calculated"); } break; case 2: Console.WriteLine("enter the side_length:"); Square shape2 = new Square(Convert.ToDouble(Console.ReadLine())); if (shape2.legal()) { Console.WriteLine("legal" + "\n and the area is " + shape2.area_calculating()); } else { Console.WriteLine("illegal" + "\n therefore, the area can not be calculated"); } break; case 3: Console.WriteLine("enter the three sides in order:"); Triangle shape3 = new Triangle(Convert.ToDouble(Console.ReadLine()), Convert.ToDouble(Console.ReadLine()), Convert.ToDouble(Console.ReadLine())); if (shape3.legal()) { Console.WriteLine("legal" + "\n and the area is " + shape3.area_calculating()); } else { Console.WriteLine("illegal" + "\n therefore, the area can not be calculated"); } break; default: goto L1; } Console.ReadKey(); }