as keyword in c sharp

as 

The as operator is used to perform certain types of conversions between compatible reference types . The as operator is like a cast operation. However, if the conversion is not possible, as returns null instead of raising an exception

Example

---

class ClassA { }

class ClassB { }

class MainClass

{

    static void Main()

    {

        object[] objArray = new object[6];

        objArray[0] = new ClassA();

        objArray[1] = new ClassB();

        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

*/