C Sharp (programming language)


C# is a general-purpose, multi-paradigm programming language encompassing strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented, and component-oriented programming disciplines. It was developed around 2000 by Microsoft as part of its.NET initiative and later approved as an international standard by Ecma in 2002 and ISO in 2003. Mono is the name of the free and open-source project to develop a compiler and runtime for the language. C# is one of the programming languages designed for the Common Language Infrastructure.
C# was designed by Anders Hejlsberg, and its development team is currently led by Mads Torgersen. The most recent version is 8.0, which was released in 2019 alongside Visual Studio 2019 version 16.3.

Design goals

The Ecma standard lists these design goals for C#:
During the development of the.NET Framework, the class libraries were originally written using a managed code compiler system called "Simple Managed C". In January 1999, Anders Hejlsberg formed a team to build a new language at the time called Cool, which stood for "C-like 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, 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, Embarcadero Delphi, and Visual J++. In interviews and technical papers he has stated that flaws in most major programming languages drove the fundamentals of the Common Language Runtime, which, in turn, drove the design of the C# language itself.
James Gosling, who created the Java programming language in 1994, and Bill Joy, a co-founder of Sun Microsystems, the originator of Java, called C# an "imitation" of Java; Gosling further said that " sort of Java with reliability, productivity and security deleted." Klaus Kreft and Angelika Langer 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 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 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 extensions released with C# 3.0 and its supporting framework of lambda expressions, extension methods, and anonymous types. 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 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 called Andy. 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.

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 where a sharp indicates that the written note should be made a semitone higher in pitch.
This is similar to the language name of C++, where "++" indicates that a variable should be incremented by 1 after being evaluated. The sharp symbol also resembles a ligature of four "+" symbols, further implying that the language is an increment of C++.
Due to technical limitations of display and the fact that the sharp symbol is not present on most keyboard layouts, the 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#, and the functional programming 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, such as Gtk# and Cocoa#.

Versions

New features

;C# 2.0
;C# 3.0
;C# 4.0
;C# 5.0
;C# 6.0
;C# 7.0
;C# 7.1
;C# 7.2
;C# 7.3
;C# 8.0
The core syntax of C# language is similar to that of other C-style languages such as C, C++ and Java. In particular:
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 . 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, or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++ or Fortran.

Typing

C# supports strongly typed implicit 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 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 .
C# is more type safe than C++. The only implicit conversions 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. Any user-defined conversion must be explicitly marked as explicit or implicit, unlike C++ copy constructors and conversion operators, which are both implicit by default.
C# has explicit support for 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.
Enumeration members are placed in their own 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 shadow variables of the enclosing block, unlike C and C++.

Metaprogramming

via C# attributes is part of the language. Many of these attributes duplicate the functionality of GCC's and VisualC++'s platform-dependent preprocessor directives.

Methods and functions

A method in C# is a member of a class that can be invoked as a function, 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 scope modifier keywords, the explicit specification of its return type, 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 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 , and has support for mutually-exclusive locks via the keyword lock.

Property

C# provides properties as syntactic sugar for a common pattern in which a pair of methods, accessor and mutator encapsulate operations on a single attribute of a class. No redundant method signatures for the getter/setter implementations need be written, and the property may be accessed using attribute syntax rather than more verbose method calls.

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 null value; it is impossible to obtain a reference to a "dead" object, 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.

Exception

are not present in C#. This has been a conscious decision based on the issues of scalability and versionability.

Polymorphism

Unlike C++, C# does not support multiple inheritance, although a class can implement any number of interfaces. This was a design decision by the language's lead architect to avoid complication and simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same signature, i. e. two methods with the same name and taking parameters of the same type in the same order, C# allows implementing each method depending on which interface that method is being called through or, like Java, allows implementing the method once, and having that be the one invocation on a call through any of the class's interfaces.
However, unlike Java, C# supports operator overloading. Only the most commonly overloaded operators in C++ may be overloaded in C#.

Language Integrated Query (LINQ)

C# has the ability to utilize LINQ through the.NET Framework. A developer can query any IEnumerable<T> object, XML documents, an ADO.NET dataset, and a SQL database. Using LINQ in C# brings advantages like 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# with 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, 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 and pattern matching.

Common type system

C# has a unified type system. This unified type system is called Common Type System.
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:
  1. Reference types
  2. Value types
Instances of value types do not 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 and cannot have an explicit default constructor. Examples of value types are all primitive types, such as , , , and . Other examples are and .
In contrast, reference types have the notion of referential identity - 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. In general, it is not always possible to create an instance of a reference type, nor to copy an existing instance, or perform 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. Examples of reference types are , , and .
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 into a value of a value type. Unboxing in C# requires an explicit type cast. A boxed object of type T can only be unboxed to a T.
Example:

int foo = 42; // Value type.
object bar = foo; // foo is boxed to bar.
int foo2 = 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, which is standardized as ECMA-335 Common Language Infrastructure .
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.

Examples

The following is a very simple C# program, a version of the classic "Hello world" example:

using System;
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.

class Program

Above is a class definition. Everything between the following pair of braces describes.

static void Main

This declares the class member method where the program begins execution. The.NET runtime calls the method. The 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, but any instance would require a program. To avoid that irresolvable circular dependency, C# compilers processing console applications report an error if there is no method. The keyword declares that has no return value.

Console.WriteLine;

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.
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.
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 Corporation, Hewlett-Packard and Intel Corporation co-sponsored the submission of specifications for C# as well as the Common Language Infrastructure to the standards organization Ecma International.
In December 2001, ECMA released ECMA-334 C# Language Specification. C# became an ISO standard in 2003. 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.
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 CLI are standardized under ISO and Ecma standards that provide reasonable and non-discriminatory licensing protection from patent claims.
Microsoft has 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. However, Novell maintains that Mono does not infringe any Microsoft patents. Microsoft has also made a specific agreement not to enforce patent rights related to the Moonlight browser plugin, which depends on Mono, provided it is obtained through Novell.

Implementations

Microsoft is leading the development of the open-source reference C# compiler and set of tools, previously codenamed "Roslyn". The compiler, which is entirely written in managed code, has been opened up and functionality surfaced as APIs. It is thus enabling developers to create refactoring and diagnostics tools.
Other C# compilers :
Mono is a common choice for game engines due to its cross-platform nature. The Unity game engine uses Mono C# as its primary scripting language. The Godot game engine has implemented an optional Mono C# module thanks to a donation of $24,000 from Microsoft.