static void Main() { Console.WriteLine("Hello World"); square s = new square(); Console.WriteLine(s.area(2,4)); for(int a = 0 ; a < 2; a++ ) { Console.WriteLine("a is :"+a); } circle c = new circle(); Console.WriteLine(c.area(10)); triangle t = new triangle(); Console.WriteLine(t.area(10,5)); string str = "Ruan"; Console.WriteLine(str.ToLower()); }