static void Main() 
 {
     int[] nums = { 1, 2, 3, 4, 5 };
     Console.Write("Original order: ");
     foreach(int i in nums)
     Console.Write(i + " ");
     Array.Reverse(nums);
     Console.Write("Reversed order: ");
     foreach(int i in nums)
     Console.Write(i + " ");
     Console.WriteLine();
 }

class B { }
class A : B { }
class Program
{
    static void Main(string[] args)
    {
        A a = new A();
        B b = new B();
        if (a is A) 
        Console.WriteLine("a is an A");
        if (b is A)
        Console.WriteLine("b is an A because it is derived from A");
        if (a is B)
        Console.WriteLine("This won’t display -- a not derived from B");
        Console.ReadLine();
    }
}

class A {}
class B : A {}
class CheckCast 
{
    static void Main() 
    {
        A a = new A();
        B b = new B();
        b = a as B;
        b = null;
        if(b==null)
        Console.WriteLine("The cast in b = (B) a is NOT allowed.");
        else
        Console.WriteLine("The cast in b = (B) a is allowed");
    }
}