A tour of the C# language

C# (pronounced "See Sharp") is a simple, modern, object-oriented, and type-safe programming language. C# has its roots in the C family of languages and will be immediately familiar to C, C++, Java, and JavaScript programmers.

This tour provides an overview of the major components of the language in C# 7 and later. If you want to explore the language through interactive examples, try the introduction to C# tutorials.

C# is an object-oriented language, but C# further includes support for component-oriented programming. Contemporary software design increasingly relies on software components in the form of self-contained and self-describing packages of functionality. Key to such components is that they present a programming model with properties, methods, and events; they have attributes that provide declarative information about the component; and they incorporate their own documentation. C# provides language constructs to support directly these concepts, making C# a very natural language in which to create and use software components.

Several C# features aid in the construction of robust and durable applications: Garbage collection automatically reclaims memory occupied by unreachable unused objects; exception handling provides a structured and extensible approach to error detection and recovery; and the type-safe design of the language makes it impossible to read from uninitialized variables, to index arrays beyond their bounds, or to perform unchecked type casts.

C# has a unified type system. All C# types, including primitive types such as int and double, inherit from a single root object type. Thus, all types share a set of common operations, and values of any type can be stored, transported, and operated upon in a consistent manner. Furthermore, C# supports both user-defined reference types and value types, allowing dynamic allocation of objects as well as in-line storage of lightweight structures.

To ensure that C# programs and libraries can evolve over time in a compatible manner, much emphasis has been placed on versioning in C#'s design. Many programming languages pay little attention to this issue, and, as a result, programs written in those languages break more often than necessary when newer versions of dependent libraries are introduced. Aspects of C#'s design that were directly influenced by versioning considerations include the separate virtual and override modifiers, the rules for method overload resolution, and support for explicit interface member declarations.

Hello world

The "Hello, World" program is traditionally used to introduce a programming language. Here it is in C#:

using System;

class Hello
    static void Main()
        Console.WriteLine("Hello, World");

C# source files typically have the file extension .cs. Assuming that the "Hello, World" program is stored in the file hello.cs, the program might be compiled using the command line:

csc hello.cs

which produces an executable assembly named hello.exe. The output produced by this application when it is run is:

Hello, World


The csc command compiles for the full framework, and may not be available on all platforms.

The "Hello, World" program starts with a using directive that references the System namespace. Namespaces provide a hierarchical means of organizing C# programs and libraries. Namespaces contain types and other namespaces—for example, the System namespace contains a number of types, such as the Console class referenced in the program, and a number of other namespaces, such as IO and Collections. A using directive that references a given namespace enables unqualified use of the types that are members of that namespace. Because of the using directive, the program can use Console.WriteLine as shorthand for System.Console.WriteLine.

The Hello class declared by the "Hello, World" program has a single member, the method named Main. The Main method is declared with the static modifier. While instance methods can reference a particular enclosing object instance using the keyword this, static methods operate without reference to a particular object. By convention, a static method named Main serves as the entry point of a program.

The output of the program is produced by the WriteLine method of the Console class in the System namespace. This class is provided by the standard class libraries, which, by default, are automatically referenced by the compiler.

Elements of the C# language

There's a lot more to learn about C#. The following topics provide an overview of the elements of the C# language. These overviews provide basic information about all elements of the language and give you the information necessary to dive deeper:

  • Program Structure
    • Learn the key organizational concepts in the C# language: programs, namespaces, types, members, and assemblies.
  • Types and Variables
    • Learn about value types, reference types, and variables in the C# language.
  • Expressions
    • Expressions are constructed from operands and operators. Expressions produce a value.
  • Statements
    • You use statements to express the actions of a program.
  • Classes and objects
    • Classes are the most fundamental of C#'s types. Objects are instances of a class. Classes are built using members, which are also covered in this topic.
  • Arrays
    • An array is a data structure that contains a number of variables that are accessed through computed indices.
  • Interfaces
    • An interface defines a contract that can be implemented by classes and structs. An interface can contain methods, properties, events, and indexers. An interface does not provide implementations of the members it defines—it merely specifies the members that must be supplied by classes or structs that implement the interface.
  • Delegates
    • A delegate type represents references to methods with a particular parameter list and return type. Delegates make it possible to treat methods as entities that can be assigned to variables and passed as parameters. Delegates are similar to the concept of function pointers found in some other languages, but unlike function pointers, delegates are object-oriented and type-safe.
  • Attributes
    • Attributes enable programs to specify additional declarative information about types, members, and other entities.


These articles apply to C# 7.0 and later. Some features may not be available in earlier versions.