IS vs AS

IS To check is the date type ?

object i = "abcd";

if(i is string)

   Console.WriteLine(i +" is string");.

AS to convert object to datatype, want to support nullable datatype.

object k = 1234;

int? x = k as int?;

• obj.ToString() - this is a call to the ToString() method of the object. The object returns a string as it was programmed to.
• obj as string - this is an attempt to convert the object to a string, which may or may not fail (if it fails, the result is null), no exception will be thrown.
• (string)obj - this is an explicit cast of obj to the type string, you are telling the compiler that obj is a string. If obj is not a string type, you will get a cast exception.
• Convert.ToString(obj) - This is an explicit call to the Convert class to return a string representation of obj.