Interface vs Abstract Class in C#

Feature	Interface	Abstract Class
Definition	An interface cannot provide any code, just the signature.	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access Modifiers	Everything Public	Can have public, private, internal for any method  , function.
Adding functionality (Versioning)	If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method.	If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.
When to use	If various implementations only share method signatures then it is better to use Interfaces.	If various implementations are of the same kind and use common behavior or status then abstract class is better to use.
Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.