Shaohen’s C# Documentation

If you want to cast an object to another type, but don’t want exceptions to be raised if the cast fails, the as operator is the choice:

expr as type

If the cast succeed: expr will be cast to type type.
If the cast fails: expr will have a null reference.

Here’s an example:

using System;

class A { }
class B : A { }

class CheckCast
    {
    public static void Main()
        {
        A a = new A();
        B b = new B();

        // replace this with
        /*
        if (a is B)
            b = (B)a;
        else
            b = null;
        */
        b = a as B;

        if (b == null)
            Console.WriteLine("Cast b = (B) a is not allowed.");
        else
            Console.WriteLine("Cast b = (B) a is allowed.");
        }
    }

(Taken from the C#: The Complete Reference by Schildt).

The cast will fail, since a is not a B;