Description:
The as operator is like a cast except that it yields null on conversion failure instead of raising an exception. More formally, an expression of the form,
	expression as type
is equivalent to,
	expression is type ? (type)expression : (type)null


Code:
// cs_keyword_as.cs
// The as operator.
using System;
class Class1
{
}

class Class2
{
}

class MainClass
{
    static void Main()
    {
        object[] objArray = new object[6];
        objArray[0] = new Class1();
        objArray[1] = new Class2();
        objArray[2] = "hello";
        objArray[3] = 123;
        objArray[4] = 123.4;
        objArray[5] = null;

        for (int i = 0; i < objArray.Length; ++i)
        {
            string s = objArray[i] as string;
            Console.Write("{0}:", i);
            if (s != null)
            {
                Console.WriteLine("'" + s + "'");
            }
            else
            {
                Console.WriteLine("not a string");
            }
        }
    }
}

Output:
0:not a string
1:not a string
2:'hello'
3:not a string
4:not a string
5:not a string