uppercasting and downcasting in c#

Consider following  two examples

1. class Employee
   {
     // some code
   }
   class Manager : Employee
   {
     //some code
   }
   class Lead : Employee
   {
     //some code
   }​

   Above we have three classes. Employee is the base class for Manager and Lead. Manager and Lead are derived classes.

2. class Shape
   {
     // some code
   }
   class Squire : Shape
   {
     //some code
   }
   class Circle : Shape
   {
     //some code
   }​

   Here we derived classes Squire and Circle from Shape

Up-Casting

Assignment of derived class object to a base class is known as up-casting. As, Up-casting is implicit any explicit typecast is not required.
For examples

Manager mgr = new Manager();
Lead ld = new Lead();
Employee emp1 = mgr;
Employee emp2 = ld;

Squire sqr = new Squire();
Circle crl = new Circle();
Shape shp1 = sqr;
Shape shp2 = crl;

Down-Casting

Assignment of base class object to derived class object is known as Down-casting. In Down-casting explicit typecast is required. Down-Casting may throw InvalidCastException.
For examples

if (employee is Manager)
{
  Manager m = (Manager)employee;
  //do something with it
}

//OR with the as operator like this:

Manager m = (employee as Manager);
if (m != null)
{
  //do something with it
}

class Employee : Person
{

}

// downcasting
Person p= new Person();
Employee e = p as Employee;

//upcasting
Employee e  = new Employee();
Person p = e as Person;

• Upcasting is an operation that creates a base class reference from a subclass reference. (subclass -> superclass) (i.e. Manager -> Employee)
• downcasting is an operation that creates a subclass reference from a base class reference. (superclass -> subclass) (i.e. Employee -> Manager)