C# is a simple, modern, object oriented, and type-safe programming language derived from C and C++. C# (pronounced “C sharp”) is firmly planted in the C and C++ family tree of languages, and will immediately be familiar to C and C++ programmers. C# aims to combine the high productivity of Visual Basic and the raw power of C++.
C# is provided as a part of Microsoft Visual Studio 7.0. In addition to C#, Visual Studio supports Visual Basic, Visual C++, and the scripting languages VBScript and JScript. All of these languages provide access to the Next Generation Windows Services (NWGS) platform, which includes a common execution engine and a rich class library. The .NET software development kit defines a "Common Language Subset" (CLS), a sort of lingua franca that ensures seamless interoperability between CLS-compliant languages and class libraries. For C# developers, this means that even though C# is a new language, it has complete access to the same rich class libraries that are used by seasoned tools such as Visual Basic and Visual C++. C# itself does not include a class library.
The rest of this chapter describes the essential features of the language. While later chapters describe rules and exceptions in a detail-oriented and sometimes mathematical manner, this chapter strives for clarity and brevity at the expense of completeness. The intent is to provide the reader with an introduction to the language that will facilitate the writing of early programs and the reading of later chapters.
1.1 Hello, world
The canonical “Hello, world” program can be written in C# as follows:
using System;
class Hello
{
    static void Main() {
        Console.WriteLine("Hello, world");
    }
}
The default file extension for C# programs is .cs, as in hello.cs. Such a program can be compiled with the command line directive
csc hello.cs
which produces an executable program named hello.exe. The output of the program is:
Hello, world
Close examination of this program is illuminating:
 The using System; directive references a namespace called System that is provided by the .NET runtime. This namespace contains the Console class referred to in the Main method. Namespaces provide a hierarchical means of organizing the elements of a class library. A “using” directive enables unqualified use of the members of a namespace. The “Hello, world” program uses Console.WriteLine as a shorthand for System.Console.WriteLine. What do these identifiers denote?  System is a namespace, Console is a class defined in that namespace, and WriteLine is a static method defined on that class.
 The Main function is a static member of the class Hello. Functions and variables are not supported at the global level; such elements are always contained within type declarations (e.g., class and struct declarations).
 The “Hello, world” output is produced through the use of a class library. C# does not itself provide a class library. Instead, C# uses a common class library that is also used by other languages such as Visual Basic and Visual C++.
For C and C++ developers, it is interesting to note a few things that do not appear in the “Hello, world” program.
 The program does not use either “::” or “->” operators. The “::” is not an operator in C# at all, and the “->” operator is used in only a small fraction of C# programs. C# programs use “.” as a separator in compound names such as Console.WriteLine.
 The program does not contain forward declarations. Forward declarations are never needed in C# programs, as declaration order is not significant.
 The program does not use #include to import program text. Dependencies between programs are handled symbolically rather than with program text. This system eliminates bar