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C# ( ) is a general-purpose,
multi-paradigm programming language Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with implications for the execution model of the language, suc ...
. C# encompasses static typing,
strong typingIn computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves tasks such as: analysis, generatin ...
,
lexically scopedIn computer programming, the scope of a name binding—an association of a name to an entity, such as a Variable (programming), variable—is the part of a Computer program, program where the name binding is valid, that is where the name can be used ...
,
imperative Imperative may refer to: *Imperative mood, a grammatical mood (or mode) expressing commands, direct requests, and prohibitions *Imperative programming, a programming paradigm in computer science *Imperative logic *Imperative (film), ''Imperative'' ...
, declarative,
functional Functional may refer to: * Movements in architecture: ** Functionalism (architecture) In architecture File:Plan d'exécution du second étage de l'hôtel de Brionne (dessin) De Cotte 2503c – Gallica 2011 (adjusted).jpg, upright=1.45, alt=Pl ...
,
generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other t ...
,
object-oriented Object-oriented programming (OOP) is a programming paradigm Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * P ...
(
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
-based), and component-oriented programming disciplines. C# was designed by
Anders Hejlsberg Anders Hejlsberg (, born 2 December 1960) is a Danish Danish may refer to: * Something of, from, or related to the country of Denmark * A national or citizen of Denmark, also called a "Dane", see Demographics of Denmark * Danish people or Danes, ...

Anders Hejlsberg
from
Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multination ...

Microsoft
in 2000 and was later approved as an
international standard An international standard is a technical standard A technical standard is an established norm Norm, the Norm or NORM may refer to: In academic disciplines * Norm (geology), an estimate of the idealised mineral content of a rock * Norm (philoso ...
by Ecma (ECMA-334) in 2002 and
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
(ISO/IEC 23270) in 2003. Microsoft introduced C# along with .NET Framework and
Visual Studio Microsoft Visual Studio is an integrated development environment#REDIRECT Integrated development environment {{Redirect category shell, 1= {{R from other capitalisation ... (IDE) from Microsoft Microsoft Corporation is an American multin ...
, both of which were
closed-source Proprietary software, also known as non-free software or closed-source software, is computer software for which the software's publisher or another person reserves some rights from licenses to use, modify, share modifications, or share the softwa ...
. At the time, Microsoft had no open-source products. Four years later, in 2004, a
free and open-source Free and open-source software (FOSS) is software that is both free software and open-source software where anyone is free software license, freely licensed to use, copy, study, and change the software in any way, and the source code is openly sh ...
project called Mono began, providing a
cross-platform In computing, cross-platform software (also multi-platform software or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software requires a separate build for each pl ...

cross-platform
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
and
runtime environment In computer programming, a runtime system, also called runtime environment, primarily implements portions of an execution model. This is not to be confused with the Run time (program lifecycle phase), runtime lifecycle phase of a program, during ...
for the C# programming language. A decade later, Microsoft released
Visual Studio Code Visual Studio Code is a source-code editor made by Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinat ...
(code editor), Roslyn (compiler), and the unified .NET platform (software framework), all of which support C# and are free, open-source, and cross-platform. Mono also joined Microsoft but was not merged into .NET. the most recent version of the language is C# 10.0, which was released in 2021 in .NET 6.0.


Design goals

The Ecma standard lists these design goals for C#: * The language is intended to be a simple, modern, general-purpose,
object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mai ...
language. * The language, and implementations thereof, should provide support for software engineering principles such as strong type checking, array
bounds checking In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves tasks such as: analysis, generati ...
, detection of attempts to use
uninitialized variableIn computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and software. ...
s, and automatic
garbage collection Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of list of waste treatment technologies, treatment or landfill. Waste collection also includes the ...
. Software robustness, durability, and programmer productivity are important. * The language is intended for use in developing
software components Component-based software engineering (CBSE), also called components-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...

software components
suitable for deployment in distributed environments. * Portability is very important for
source code In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and ...

source code
and , especially those already familiar with C and
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
. * Support for
internationalization In economics, internationalization or internationalisation is the process of increasing involvement of enterprises in international markets, although there is no agreed definition of internationalization. Internationalization is a crucial strategy ...
is very important. * C# is intended to be suitable for writing applications for both hosted and
embedded system An embedded system is a computer system A computer is a machine that can be programmed to carry out Sequence, sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Co ...
s, ranging from the very large that use sophisticated
operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, Android (operating system), Android and Mi ...

operating system
s, down to the very small having dedicated functions. * Although C# applications are intended to be economical with regard to memory and
processing power In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwar ...
requirements, the language was not intended to compete directly on performance and size with C or assembly language.


History

During the development of the .NET Framework, the class libraries were originally written using a
managed code Managed code is computer program code that requires and will execute only under the management of a Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification and technical standard originally developed by ...
compiler system called ''" Simple Managed C"'' (SMC). In January 1999,
Anders Hejlsberg Anders Hejlsberg (, born 2 December 1960) is a Danish Danish may refer to: * Something of, from, or related to the country of Denmark * A national or citizen of Denmark, also called a "Dane", see Demographics of Denmark * Danish people or Danes, ...

Anders Hejlsberg
formed a team to build a new language at the time called Cool, which stood for "
C-like Due to the success of the C (programming language), C programming language and some of its derivatives, C-family programming languages span a large variety of programming paradigms, conceptual models, and run-time environments. References

...
Object Oriented Language". Microsoft had considered keeping the name "Cool" as the final name of the language, but chose not to do so for trademark reasons. By the time the .NET project was publicly announced at the July 2000
Professional Developers Conference Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company with headquarters in Redmond, Washington. It develops, manufactures, licenses, supports, and sells Software, computer software, consumer ...
, the language had been renamed C#, and the class libraries and ASP.NET runtime had been ported to C#. Hejlsberg is C#'s principal designer and lead architect at Microsoft, and was previously involved with the design of
Turbo Pascal Turbo Pascal is a software development system that includes a compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into ano ...
,
Embarcadero Delphi Delphi is a software product that uses the Delphi dialect of the Object Pascal Object Pascal is an extension to the programming language Pascal that provides object-oriented programming Object-oriented programming (OOP) is a programming pa ...
(formerly CodeGear Delphi, Inprise Delphi and Borland Delphi), and
Visual J++ Visual J++ ''(pronounced "Jay Plus Plus")'' is Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational fo ...
. In interviews and technical papers he has stated that flaws in most major programming languages (e.g.
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
,
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
,
Delphi Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The oracle ...
, and
Smalltalk Smalltalk is an object-oriented programming, object-oriented, dynamically typed reflection (computer science), reflective programming language. Smalltalk was created as the language underpinning the "new world" of computing exemplified by "human ...

Smalltalk
) drove the fundamentals of the
Common Language Runtime The Common Language Runtime (CLR), the virtual machine component of Microsoft .NET Framework, manages the execution of .NET programs. Just-in-time compilation converts the managed code (compiled intermediate language code) into machine instructio ...

Common Language Runtime
(CLR), which, in turn, drove the design of the C# language itself.
James Gosling James Arthur Gosling, often referred to as "Dr. Java," Order of Canada, OC (born May 19, 1955) is a Canadian computer scientist, best known as the founder and lead designer behind the Java (programming language), Java programming language. Gosli ...
, who created the
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
programming language in 1994, and
Bill Joy William Nelson Joy (born November 8, 1954) is an American computer engineer and venture capitalist. He co-founded Sun Microsystems in 1982 along with Scott McNealy, Vinod Khosla, and Andy Bechtolsheim, and served as Chief Scientist and CTO at th ...

Bill Joy
, a co-founder of
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. M ...
, the originator of Java, called C# an "imitation" of Java; Gosling further said that " # issort of Java with reliability, productivity and security deleted." Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that "Java and C# are almost identical programming languages. Boring repetition that lacks innovation," "Hardly anybody will claim that Java or C# are revolutionary programming languages that changed the way we write programs," and "C# borrowed a lot from Java - and vice versa. Now that C# supports
boxing Boxing is a combat sport A combat sport, or fighting sport, is a competitive contact sport that usually involves one-on-one combat. In many combat sports, a contestant wins by scoring more points than the opponent or by disabling the opponent ...
and unboxing, we'll have a very similar feature in Java." In July 2000, Hejlsberg said that C# is "not a Java clone" and is "much closer to C++" in its design. Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming two quite different languages. One of the first major departures came with the addition of generics to both languages, with vastly different implementations. C# makes use of
reification Reification may refer to: Science and technology * Reification (computer science), the creation of a data model * Reification (knowledge representation), the representation of facts and/or assertions * Reification (statistics), the use of an ideali ...
to provide "first-class" generic objects that can be used like any other class, with code generation performed at class-load time. Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the
LINQ Language Integrated Query (LINQ, pronounced "link") is a Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company with headquarters in Redmond, Washington. It develops, manufactures, licenses, ...
extensions released with C# 3.0 and its supporting framework of
lambda expressions Lambda calculus (also written as λ-calculus) is a formal system A formal system is used for inferring theorems from axioms according to a set of rules. These rules, which are used for carrying out the inference of theorems from axioms, are the logi ...
,
extension method In object-oriented computer programming, an extension method is a method Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more oft ...
s, and
anonymous type Anonymous may refer to: * Anonymity, the state of an individual's identity, or personally identifiable information, being publicly unknown ** Anonymous work, a work of art or literature that has an unnamed or unknown creator or author Organiza ...
s. These features enable C# programmers to use functional programming techniques, such as closures, when it is advantageous to their application. The LINQ extensions and the functional imports help developers reduce the amount of
boilerplate code In computer programming, boilerplate code or just boilerplate are sections of code that are repeated in multiple places with little to no variation. When using languages that are considered ''verbose'', the programmer must write a lot of code to ac ...
that is included in common tasks like querying a database, parsing an xml file, or searching through a data structure, shifting the emphasis onto the actual program logic to help improve readability and maintainability. C# used to have a
mascot A mascot is any human, animal, or object thought to bring luck Luck is the phenomenon and belief that defines the experience of notably positive, negative, or improbable events. The naturalistic interpretation is that positive and negative ...

mascot
called Andy (named after Anders Hejlsberg). It was retired on January 29, 2004. C# was originally submitted to the ISO subcommittee JTC 1/SC 22 for review, under ISO/IEC 23270:2003, was withdrawn and was then approved under ISO/IEC 23270:2006. The 23270:2006 is withdrawn under 23270:2018 and approved with this version.


Name

Microsoft first used the name C# in 1988 for a variant of the C language designed for incremental compilation. That project was not completed but the name lives on. The name "C sharp" was inspired by the musical notation whereby a sharp symbol indicates that the written note should be made a
semitone A semitone, also called a half step or a half tone, is the smallest musical interval In music theory Music theory is the study of the practices and possibilities of music. ''The Oxford Companion to Music'' describes three interrelated us ...
higher in
pitch Pitch may refer to: Acoustic frequency * Pitch (music), the perceived frequency of sound including "definite pitch" and "indefinite pitch" ** Absolute pitch or "perfect pitch" ** Pitch class, a set of all pitches that are a whole number of octaves ...
. This is similar to the language name of
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
, where "++" indicates that a variable should be incremented by 1 after being evaluated. The sharp symbol also resembles a
ligature Ligature may refer to: * Ligature (medicine), a piece of suture used to shut off a blood vessel or other anatomical structure ** Ligature (orthodontic), used in dentistry * Ligature (music), an element of musical notation used especially in the med ...
of four "+" symbols (in a two-by-two grid), further implying that the language is an increment of C++. Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol () is not present on most
keyboard layout A keyboard layout is any specific physical, visual or functional arrangement of the keys, legends, or key-meaning associations (respectively) of a computer keyboard A computer keyboard is a peripheral A peripheral or peripheral device is an ...
s, the
number sign The symbol is known variously in English-speaking regions as the number sign, hash, or pound sign. The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a Typographic ligature, ...

number sign
() was chosen to approximate the sharp symbol in the written name of the programming language. This convention is reflected in the ECMA-334 C# Language Specification. The "sharp" suffix has been used by a number of other .NET languages that are variants of existing languages, including J# (a .NET language also designed by Microsoft that is derived from Java 1.1), A# (from
Ada Ada may refer to: Places Africa * Ada Foah Ada Foah is a town on the southeast coast of Ghana, where the Volta River meets the Atlantic Ocean. The town is located along the Volta River, off of the Accra-Aflao motorway. Known for Palm tree, pal ...
), and the
functional programming In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
language F#. The original implementation of Eiffel for .NET was called Eiffel#, a name retired since the full Eiffel language is now supported. The suffix has also been used for
libraries A library is a collection of materials, books or media that are easily accessible for use and not just for display purposes. It is responsible for housing updated information in order to meet the user's needs on a daily basis. A library provi ...
, such as Gtk# (a .NET wrapper for
GTK GTK (formerly GIMP ToolKit then GTK+) is a free and open-source cross-platform widget toolkit for creating graphical user interfaces (GUIs). It is licensed under the terms of the GNU Lesser General Public License, allowing both Free software, fr ...

GTK
and other
GNOME A gnome is a mythological creature A legendary or mythological creature, also called fabulous creature and fabulous beast, is a supernatural The supernatural encompasses supposed phenomena that are not subject to the laws of nature.htt ...

GNOME
libraries) and Cocoa# (a wrapper for
Cocoa CoCoA (Computations in Commutative Algebra) is a free computer algebra system developed by the University of Genova, Italy, used to compute with numbers and polynomials. The CoCoA Library (CoCoALib) is available under GNU General Public License. ...
).


Versions


Syntax

The core syntax of the C# language is similar to that of other C-style languages such as C, C++ and Java, particularly: * Semicolons are used to denote the end of a statement. *
Curly brackets A bracket is either of two tall fore- or back-facing punctuation Punctuation (or sometimes interpunction) is the use of spacing, conventional signs (called punctuation marks), and certain typographical devices as aids to the understanding ...
are used to group statements. Statements are commonly grouped into methods (functions), methods into classes, and classes into
namespaces In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...
. * Variables are assigned using an
equals sign The equals sign (, ) or equal sign (), formerly known as the equality sign, is the , which is used to indicate in some sense. In an , it is placed between two that have the same value, or for which one studies the conditions under which the ...

equals sign
, but compared using two consecutive equals signs. *
Square brackets A bracket is either of two tall fore- or back-facing punctuation Punctuation (or sometimes interpunction) is the use of spacing, conventional signs (called punctuation marks), and certain typographical devices as aids to the understanding ...

Square brackets
are used with
arrays ARRAY, also known as ARRAY Now, is an independent distribution company launched by film maker and former publicist Ava DuVernay Ava Marie DuVernay (; born August 24, 1972) is an American filmmaker. She won the directing award in the U.S. drama ...
, both to declare them and to get a value at a given index in one of them.


Distinguishing features

Some notable features of C# that distinguish it from C, C++, and Java where noted, are:


Portability

By design, C# is the programming language that most directly reflects the underlying
Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard ...
 (CLI). Most of its intrinsic types correspond to value-types implemented by the CLI framework. However, the language specification does not state the code generation requirements of the compiler: that is, it does not state that a C# compiler must target a Common Language Runtime, or generate
Common Intermediate Language Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL) or Intermediate Language (IL), is the intermediate language binary instruction set defined within the Common Language Infrastructure The Common Languag ...
(CIL), or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++ or
Fortran Fortran (; formerly FORTRAN) is a general-purpose, compiled language, compiled imperative programming, imperative programming language that is especially suited to numerical analysis, numeric computation and computational science, scientific com ...

Fortran
.


Typing

C# supports strongly, implicitly typed variable declarations with the keyword var, and implicitly typed arrays with the keyword new[] followed by a collection initializer. C# supports a strict Boolean data type, bool. Statements that take conditions, such as while and if, require an expression of a type that implements the true operator, such as the Boolean type. While C++ also has a Boolean type, it can be freely converted to and from integers, and expressions such as if (a) require only that a is convertible to bool, allowing a to be an int, or a pointer. C# disallows this "integer meaning true or false" approach, on the grounds that forcing programmers to use expressions that return exactly bool can prevent certain types of programming mistakes such as if (a = b) (use of assignment = instead of equality

). C# is more type safe than C++. The only
implicit conversion In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
s by default are those that are considered safe, such as widening of integers. This is enforced at compile-time, during JIT, and, in some cases, at runtime. No implicit conversions occur between Booleans and integers, nor between enumeration members and integers (except for literal 0, which can be implicitly converted to any enumerated type). Any user-defined conversion must be explicitly marked as explicit or implicit, unlike C++
copy constructor In class-based object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "Object (computer science), objects", which can contain data and code: data in the form of Field (computer science ...
s and conversion operators, which are both implicit by default. C# has explicit support for Covariance and contravariance (computer science), covariance and contravariance in generic types, unlike C++ which has some degree of support for contravariance simply through the semantics of return types on virtual methods. enumerated type, Enumeration members are placed in their own Scope (programming), scope. The C# language does not allow for global variables or functions. All methods and members must be declared within classes. Static members of public classes can substitute for global variables and functions. Local variables cannot Variable shadowing, shadow variables of the enclosing block, unlike C and C++.


Metaprogramming

Metaprogramming can be achieved in several ways: * Reflective_programming, Reflection using framework API * Expression tree language feature represents code as an abstract syntax tree, where each node is an expression that can be inspected or executed. This enables dynamic modification of executable code at runtime. Expression tree introduced some homoiconicity to the language. * Attribute_(computing), Attribute language feature are metadata attached to a field or a block of code like Assembly (programming), assemblies, Member variable, members and Data type, types, and are equivalent to Java annotation, annotations in Java. Attributes are accessible to both the compiler and programmatically through Reflection (computer programming), reflection. Many of these attributes duplicate the functionality of GCC's and VisualC++'s platform-dependent preprocessor directives. * Source generators, feature of Roslyn_(compiler), Roslyn C#
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
, enable compile time metaprogramming. During the compilation process, developers can inspect the code being compiled (using compiler API) and generate new C# source files that can be added to the compilation.


Methods and functions

A method in C# is a member of a class that can be invoked as a function (a sequence of instructions), rather than the mere value-holding capability of a class property. As in other syntactically similar languages, such as C++ and ANSI C, the signature of a method is a declaration comprising in order: any optional accessibility keywords (such as private), the explicit specification of its return type (such as int, or the keyword void if no value is returned), the name of the method, and finally, a parenthesized sequence of comma-separated parameter specifications, each consisting of a parameter's type, its formal name and optionally, a default value to be used whenever none is provided. Certain specific kinds of methods, such as those that simply get or set a class property by return value or assignment, do not require a full signature, but in the general case, the definition of a class includes the full signature declaration of its methods. Like C++, and unlike Java, C# programmers must use the scope modifier keyword virtual to allow methods to be method overriding, overridden by subclasses. ''Extension methods'' in C# allow programmers to use static methods as if they were methods from a class's method table, allowing programmers to add methods to an object that they feel should exist on that object and its derivatives. The type dynamic allows for run-time method binding, allowing for JavaScript-like method calls and run-time object composition. C# has support for strongly-typed function pointers via the keyword delegate. Like the Qt framework's pseudo-C++ ''signal'' and ''slot'', C# has semantics specifically surrounding publish-subscribe style events, though C# uses delegates to do so. C# offers Java-like synchronized method calls, via the attribute [MethodImpl(MethodImplOptions.Synchronized)], and has support for Mutual exclusion, mutually-exclusive locks via the keyword lock.


Property

C# supports classes with property (programming), properties. The properties can be simple accessor functions with a backing field, or implement getter and setter functions. Since C# 3.0 the syntactic sugar of auto-implemented properties is available, where the Mutator method, accessor (getter) and mutator (setter) encapsulate operations on a single Attribute (computing), attribute of a class.


Namespace

A C# namespace provides the same level of code isolation as a Java package or a C++ , with very similar rules and features to a package. Namespaces can be imported with the "using" syntax.


Memory access

In C#, memory address pointers can only be used within blocks specifically marked as ''unsafe'', and programs with unsafe code need appropriate permissions to run. Most object access is done through safe object references, which always either point to a "live" object or have the well-defined Nullable type, null value; it is impossible to obtain a reference to a "dead" object (one that has been garbage collected), or to a random block of memory. An unsafe pointer can point to an instance of an 'unmanaged' value type that does not contain any references to garbage-collected objects, array, string, or a block of stack-allocated memory. Code that is not marked as unsafe can still store and manipulate pointers through the System.IntPtr type, but it cannot dereference them. Managed memory cannot be explicitly freed; instead, it is automatically garbage collected. Garbage collection addresses the problem of memory leaks by freeing the programmer of responsibility for releasing memory that is no longer needed in most cases. Code that retains references to objects longer than is required can still experience higher memory usage than necessary, however once the final reference to an object is released the memory is available for garbage collection.


Exception

A range of standard exceptions are available to programmers. Methods in standard libraries regularly throw system exceptions in some circumstances and the range of exceptions thrown is normally documented. Custom exception classes can be defined for classes allowing specific handling to be put in place for particular circumstances as needed. Checked exceptions are not present in C# (in contrast to Java). This has been a conscious decision based on the issues of scalability and versionability.


Polymorphism

Unlike
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
, C# does not support multiple inheritance, although a class can implement any number of "Protocol (object-oriented programming), interfaces" (fully abstract classes). This was a design decision by the language's lead architect to avoid complications and to simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same name and taking parameters of the same type in the same order (i.e. the same Type signature, signature), similar to
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
, C# allows both a single method to cover all interfaces and if necessary specific methods for each interface. However, unlike Java, C# supports operator overloading.


Language Integrated Query (LINQ)

C# has the ability to utilize
LINQ Language Integrated Query (LINQ, pronounced "link") is a Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company with headquarters in Redmond, Washington. It develops, manufactures, licenses, ...
through the .NET Framework. A developer can query a variety of data sources, provided IEnumerable<T> interface is implemented on the object. This includes XML documents, an ADO.NET dataset, and SQL databases. Using LINQ in C# brings advantages like Intelligent code completion, Intellisense support, strong filtering capabilities, type safety with compile error checking ability, and consistency for querying data over a variety of sources. There are several different language structures that can be utilized with C# and LINQ and they are query expressions, lambda expressions, anonymous types, implicitly typed variables, extension methods, and object initializers.


Functional programming

Though primarily an imperative language, C# 2.0 offered limited support for functional programming through first-class functions and closures in the form of anonymous delegates. C# 3.0 expanded support for functional programming with the introduction of a lightweight syntax for lambda expressions, extension methods (an affordance for modules), and a list comprehension syntax in the form of a "query comprehension" language. C# 7.0 adds features typically found in functional languages like tuples, local functions and pattern matching. C# 9.0 introduces record feature which is primarily built for better supporting immutable data models.


Common type system

C# has a ''unified type system''. This unified type system is called Common Type System (CTS). A unified type system implies that all types, including primitives such as integers, are subclasses of the class. For example, every type inherits a method.


Categories of data types

CTS separates data types into two categories: # Reference types # Value types Instances of value types neither have referential identity nor referential comparison semantics. Equality and inequality comparisons for value types compare the actual data values within the instances, unless the corresponding operators are overloaded. Value types are derived from , always have a default value, and can always be created and copied. Some other limitations on value types are that they cannot derive from each other (but can implement interfaces) and cannot have an explicit default (parameterless) constructor. Examples of value types are all primitive types, such as (a signed 32-bit integer), (a 32-bit IEEE floating-point number), (a 16-bit Unicode code unit), and (identifies a specific point in time with nanosecond precision). Other examples are (enumerations) and (user defined structures). In contrast, reference types have the notion of referential identity, meaning that each instance of a reference type is inherently distinct from every other instance, even if the data within both instances is the same. This is reflected in default equality and inequality comparisons for reference types, which test for referential rather than structural equality, unless the corresponding operators are overloaded (such as the case for ). Some operations are not always possible, such as creating an instance of a reference type, copying an existing instance, or performing a value comparison on two existing instances. Though specific reference types can provide such services by exposing a public constructor or implementing a corresponding interface (such as or ). Examples of reference types are (the ultimate base class for all other C# classes), (a string of Unicode characters), and (a base class for all C# arrays). Both type categories are extensible with user-defined types.


Boxing and unboxing

''Boxing'' is the operation of converting a value-type object into a value of a corresponding reference type. Boxing in C# is implicit. ''Unboxing'' is the operation of converting a value of a reference type (previously boxed) into a value of a value type. Unboxing in C# requires an explicit Type conversion, type cast. A boxed object of type T can only be unboxed to a T (or a nullable T). Example: int foo = 42; // Value type. object bar = foo; // foo is boxed to bar. int foo2 = (int)bar; // Unboxed back to value type.


Libraries

The C# specification details a minimum set of types and class libraries that the compiler expects to have available. In practice, C# is most often used with some implementation of the
Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard ...
(CLI), which is standardized as ECMA-335 ''Common Language Infrastructure (CLI)''. In addition to the standard CLI specifications, there are many commercial and community class libraries that build on top of the .NET framework libraries to provide additional functionality. C# can make calls to any library included in the List of .NET libraries and frameworks.


Examples


Hello World

The following is a very simple C# program, a version of the classic "Hello world" example using the top-level statements feature introduced in C# 9: using System; Console.WriteLine("Hello, world!"); For code written as C# 8 or lower, the entry point logic of a program must be written in a Main method inside a type: using System; // A version of the classic "Hello World" program class Program This code will display this text in the console window: Hello, world! Each line has a purpose: using System; The above line imports all types in the System namespace. For example, the Console class used later in the source code is defined in the System namespace, meaning it can be used without supplying the full name of the type (which includes the namespace). // A version of the classic "Hello World" program This line is a comment; it describes and documents the code for the programmer(s). class Program Above is a
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
definition for the class. Everything that follows between the pair of braces describes that class. The curly brackets demarcate the boundaries of a code block. In this first instance, they are marking the start and end of the class. static void Main(string[] args) This declares the class member method where the program begins execution. The .NET runtime calls the method. Unlike in
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
, the method does not need the keyword, which tells the compiler that the method can be called from anywhere by any class. Writing is equivalent to writing . The Method (computer programming)#Static methods, static keyword makes the method accessible without an instance of . Each console application's entry point must be declared otherwise the program would require an instance of , but any instance would require a program. To avoid that irresolvable circular dependency, C# compilers processing console applications (like that above) report an error if there is no method. The keyword declares that has no return value. Console.WriteLine("Hello, world!"); This line writes the output. is a static class in the namespace. It provides an interface to the standard input, output, and error streams for console applications. The program calls the method , which displays on the console a line with the argument, the string .


GUI

A GUI example: using System; using System.Windows.Forms; class Program This example is similar to the previous example, except that it generates a dialog box that contains the message "Hello, World!" instead of writing it to the console.


Images

Another useful library is the System.Drawing library, which is used to programmatically draw images. For example: using System; using System.Drawing; public class Example This will create an image that is identical to that stored in "Image.png".


Standardization and licensing

In August 2001,
Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multination ...

Microsoft
, Hewlett-Packard and Intel co-sponsored the submission of specifications for C# as well as the Common Language Infrastructure, Common Language Infrastructure (CLI) to the standards organization Ecma International. In December 2001, ECMA released ECMA-334 ''C# Language Specification''. C# became an
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
standard in 2003 (ISO/IEC 23270:2003 - ''Information technology — Programming languages — C#''). ECMA had previously adopted equivalent specifications as the 2nd edition of C#, in December 2002. In June 2005, ECMA approved edition 3 of the C# specification, and updated ECMA-334. Additions included partial classes, anonymous methods, nullable types, and generics (somewhat similar to C++ template (programming), templates). In July 2005, ECMA submitted to ISO/IEC JTC 1, via the latter's Fast-Track process, the standards and related TRs. This process usually takes 6–9 months. The C# language definition and the Common Language Infrastructure, CLI are standardized under
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
and Ecma standards that provide Reasonable and Non Discriminatory Licensing, reasonable and non-discriminatory licensing protection from patent claims. Microsoft initially agreed not to sue open-source developers for violating patents in non-profit projects for the part of the framework that is covered by the OSP. Microsoft has also agreed not to enforce patents relating to Novell products against Novell's paying customers with the exception of a list of products that do not explicitly mention C#, .NET or Novell's implementation of .NET (Mono (software), The Mono Project). However, Novell maintained that Mono does not infringe any Microsoft patents. Microsoft also made a specific agreement not to enforce patent rights related to the Moonlight (runtime), Moonlight browser plugin, which depends on Mono, provided it is obtained through Novell. A decade later, Microsoft began developing free, open-source, and cross-platform tooling for C#, namely
Visual Studio Code Visual Studio Code is a source-code editor made by Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinat ...
, .NET Core, and Roslyn. Mono joined Microsoft as a project of Xamarin, a Microsoft subsidiary.


Implementations

Microsoft is leading the development of the Open-source software, open-source reference C# compilers and set of tools. The first compiler, Microsoft Roslyn, Roslyn, compiles into intermediate language (IL), and the second one, RyuJIT, is a JIT (just-in-time) compiler, which is dynamic and does on-the-fly optimization and compiles the IL into native code for the front-end of the CPU. RyuJIT is open source and written in C++. Roslyn is entirely written in
managed code Managed code is computer program code that requires and will execute only under the management of a Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification and technical standard originally developed by ...
(C#), has been opened up and functionality surfaced as APIs. It is thus enabling developers to create refactoring and diagnostics tools. Two branches of official implementation are .NET Framework (closed-source, Windows-only) and .NET Core (open-source, cross-platform); they eventually converged into one open-source implementation: .NET 5.0. At .NET Framework 4.6, a new JIT compiler replaced the former. Other C# compilers (some of which include an implementation of the
Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard ...
and .NET class libraries): * Mono, a Microsoft-sponsored project provides an open-source C# compiler, a complete open-source implementation of the CLI (including the required framework libraries as they appear in the ECMA specification,) and a nearly complete implementation of the NET class libraries up to .NET Framework 3.5. * The RemObjects Elements, Elements tool chain from RemObjects includes RemObjects C#, which compiles C# code to .NET's
Common Intermediate Language Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL) or Intermediate Language (IL), is the intermediate language binary instruction set defined within the Common Language Infrastructure The Common Languag ...
, Java bytecode,
Cocoa CoCoA (Computations in Commutative Algebra) is a free computer algebra system developed by the University of Genova, Italy, used to compute with numbers and polynomials. The CoCoA Library (CoCoALib) is available under GNU General Public License. ...
, Dalvik (software), Android bytecode, WebAssembly, and native machine code for Windows, macOS, and Linux. *The DotGNU project (now discontinued) also provided an open-source C# compiler, a nearly complete implementation of the Common Language Infrastructure including the required framework libraries as they appear in the ECMA specification, and subset of some of the remaining Microsoft proprietary .NET class libraries up to .NET 2.0 (those not documented or included in the ECMA specification, but included in Microsoft's standard .NET Framework distribution). The Unity (game engine), Unity game engine uses C# as its primary scripting language. The Godot (game engine), Godot game engine has implemented an optional C# module thanks to a donation of $24,000 from Microsoft.


See also

;C# topics * C Sharp syntax, C# syntax * Comparison of C Sharp and Java, Comparison of C# and Java * Comparison of C Sharp and Visual Basic .NET, Comparison of C# and Visual Basic .NET * Standard Libraries (CLI), .NET standard libraries ;IDEs * Microsoft Visual Studio * Microsoft Visual Studio Express *
Visual Studio Code Visual Studio Code is a source-code editor made by Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinat ...
* MonoDevelop * Morfik * SharpDevelop * Turbo C Sharp, Turbo C# * JetBrains#Rider, Rider * Xamarin Studio * LINQPad


Notes


References


Further reading

* *


External links


C# Language Specification

C# Programming Guide

ISO C# Language Specification

C# Compiler Platform ("Roslyn") source code
{{Authority control American inventions Programming languages C Sharp programming language family, .NET programming languages Class-based programming languages Ecma standards Functional languages IEC standards ISO standards Microsoft programming languages Multi-paradigm programming languages Programming languages created in 2000 Programming languages with an ISO standard Statically typed programming languages 2000 software