How can I check the type of an object at runtime? | C#.Net Interview Questions

You can use the is keyword. For example:
using System;
class CApp
{
public static void Main()
{
  string s = "fred";
  long i = 10;
  Console.WriteLine("{0} is {1}an integer",s,(IsInteger(s)? "" :"not") );
  Console.WriteLine("{0} is {1}an integer",i,(IsInteger(i)? "" :"not") );
}
static bool IsInteger( object obj )
{
  if( obj is int || obj is long )
  return true;
  else
  return false;
}
}
produces the output:
fred is not an integer
10 is an integer.