.Net FAQ's
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.Net Faq's
Structures are value type and Classes are reference type
Structures can not have contractors or destructors.
Classes can have both contractors and destructors.
Structures do not support Inheritance, while Classes support Inheritance.
Class : is logical representation of object. It is collection of data and related sub procedures with defination.
Interface : is also a class containg methods which is not having any definations.Class does not support multiple inheritance. But interface can support.
Delegates are a type-safe, object-oriented implementation of function pointers and are used in many situations where a component needs to call back to the component that is using it.
Authentication is the process of identifying users. Authentication is identifying/validating the user against the credentials (username and password).
Authorization performs after authentication. Authorization is the process of granting access to those users based on identity. Authorization allowing access of specific resource to user.
A class declaration may specify a base class by following the class name with a colon and the name of the base class. omitting a base class specification is the same as deriving from type object.
No 'This' cannot be used in a static method. As only static variables/methods can be used in a static method.
Constants: The value can't be changed.
Read-only: The value will be initialized only once from the constructor of the class.
Static: Value can be initialized once.
C# supports several different kinds of statements are 
Block statements
Declaration statements
Expression statements
Selection statements
Iteration statements
Jump statements
Try catch statements
Checked and unchecked
Lock statement
It is an abstract class with public abstract methods all of which must be implemented in the inherited classes.
Value types are stored in the Stack.
Examples : bool, byte, chat, decimal, double, enum , float, int, long, sbyte, short, strut, uint, ulong, ushort.
Reference types are stored in the Heap. 
Examples : class, delegate, interface, object, string.