using System; class App { public static void Main(){ BankAccount ba1 = new BankAccount("George", 1000.0M, 0.01), ba2 = new CheckAccount("Bill", 2000.0M, 0.01), baRes1, baRes2, baRes3, baRes4, baRes5, baRes6; CheckAccount ca = new CheckAccount("John", 2000.0M, 0.01); baRes1 = ba1 as BankAccount; Report(baRes1); baRes2 = ba1 as CheckAccount; Report(baRes2); // null is reported baRes3 = ba2 as BankAccount; Report(baRes3); baRes4 = ba2 as CheckAccount; Report(baRes4); baRes5 = ca as BankAccount; Report(baRes5); baRes6 = ca as CheckAccount; Report(baRes6); } public static void Report(BankAccount ba){ if (ba != null) Console.WriteLine("{0}", ba); else Console.WriteLine("null"); } }