The C# language is disarmingly simple, with only about 80 keywords and a dozen built-in datatypes, but C# is highly expressive when it comes to implementing modern programming concepts. C# includes all the support for structured, component-based, object-oriented programming that one expects of a modern language built on the shoulders of C++ and Java.
The C# language was developed by a small team led by two distinguished Microsoft engineers, Anders Hejlsberg and Scott Wiltamuth. Hejlsberg is also known for creating Turbo Pascal, a popular language for PC programming, and for leading the team that designed Borland Delphi, one of the first successful integrated development environments for client/server programming.
At the heart of any object-oriented language is its support for defining and working with classes. Classes define new types, allowing you to extend the language to better model the problem you are trying to solve. C# contains keywords for declaring new classes and their methods and properties, and for implementing encapsulation, inheritance, and polymorphism, the three pillars of object-oriented programming.
In C#, everything pertaining to a class declaration is found in the declaration itself. C# class definitions do not require separate header files or Interface Definition Language (IDL) files. Moreover, C# supports a new XML style of inline documentation that simplifies the creation of online and print reference documentation for an application.
C# also supports interfaces, a means of making a contract with a class for services that the interface stipulates. In C#, a class can inherit from only a single parent, but a class can implement multiple interfaces. When it implements an interface, a C# class in effect promises to provide the functionality the interface specifies.
C# also provides support for structs, a concept whose meaning has changed significantly from C++. In C#, a struct is a restricted, lightweight type that, when instantiated, makes fewer demands on the operating system and on memory than a conventional class does. A struct can't inherit from a class or be inherited from, but a struct can implement an interface.
C# provides component-oriented features, such as properties, events, and declarative constructs (called attributes). Component-oriented programming is supported by the CLR's support for storing metadata with the code for the class. The metadata describes the class, including its methods and properties, as well as its security needs and other attributes, such as whether it can be serialized; the code contains the logic necessary to carry out its functions. A compiled class is thus a self-contained unit. Therefore, a hosting environment that knows how to read a class' metadata and code needs no other information to make use of it. Using C# and the CLR, it is possible to add custom metadata to a class by creating custom attributes. Likewise, it is possible to read class metadata using CLR types that support reflection.
An assembly is a collection of files that appear to the programmer to be a single dynamic link library (DLL) or executable (EXE). In .NET, an assembly is the basic unit of reuse, versioning, security, and deployment. The CLR provides a number of classes for manipulating assemblies.
A final note about C# is that it also provides support for directly accessing memory using C++ style pointers and keywords for bracketing such operations as unsafe, and for warning the CLR garbage collector not to collect objects referenced by pointers until they are released.