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88-416: The C-family programming languages share significant features of the C programming language . Many were developmentally influenced by C due to its success and ubiquity. The family also includes predecessors that influenced C's design such as BCPL . Notable programming sources use terms like C-style , C-like , a dialect of C , having C-like syntax . The term curly bracket programming language denotes
176-402: A declarative and composable style, where small functions are combined in a modular manner. Functional programming is sometimes treated as synonymous with purely functional programming , a subset of functional programming that treats all functions as deterministic mathematical functions , or pure functions . When a pure function is called with some given arguments, it will always return
264-540: A static type system . It was designed to be compiled to provide low-level access to memory and language constructs that map efficiently to machine instructions , all with minimal runtime support . Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards -compliant C program written with portability in mind can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code. Since 2000, C has consistently ranked among
352-614: A bank account balance) that often seem most naturally implemented with state. Pure functional programming performs these tasks, and I/O tasks such as accepting user input and printing to the screen, in a different way. The pure functional programming language Haskell implements them using monads , derived from category theory . Monads offer a way to abstract certain types of computational patterns, including (but not limited to) modeling of computations with mutable state (and other side effects such as I/O) in an imperative manner without losing purity. While existing monads may be easy to apply in
440-452: A certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness . In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to prevent
528-408: A cleanly functional core, while Common Lisp was designed to preserve and update the paradigmatic features of the numerous older dialects it replaced. Information Processing Language (IPL), 1956, is sometimes cited as the first computer-based functional programming language. It is an assembly-style language for manipulating lists of symbols. It does have a notion of generator , which amounts to
616-415: A compiler into the same code used to implement iteration in imperative languages. Tail recursion optimization can be implemented by transforming the program into continuation passing style during compiling, among other approaches. The Scheme language standard requires implementations to support proper tail recursion, meaning they must allow an unbounded number of active tail calls. Proper tail recursion
704-569: A consequence, these languages fail to be Turing complete and expressing certain functions in them is impossible, but they can still express a wide class of interesting computations while avoiding the problems introduced by unrestricted recursion. Functional programming limited to well-founded recursion with a few other constraints is called total functional programming . Functional languages can be categorized by whether they use strict (eager) or non-strict (lazy) evaluation, concepts that refer to how function arguments are processed when an expression
792-540: A correspondence between ALGOL 60 and the lambda calculus , and proposed the ISWIM programming language. John Backus presented FP in his 1977 Turing Award lecture "Can Programming Be Liberated From the von Neumann Style? A Functional Style and its Algebra of Programs". He defines functional programs as being built up in a hierarchical way by means of "combining forms" that allow an "algebra of programs"; in modern language, this means that functional programs follow
880-408: A function that accepts a function as an argument, and, since it is an assembly-level language, code can be data, so IPL can be regarded as having higher-order functions. However, it relies heavily on the mutating list structure and similar imperative features. Kenneth E. Iverson developed APL in the early 1960s, described in his 1962 book A Programming Language ( ISBN 9780471430148 ). APL
968-471: A functional style or have implemented features from functional programming, such as C++11 , C# , Kotlin , Perl , PHP , Python , Go , Rust , Raku , Scala , and Java (since Java 8) . The lambda calculus , developed in the 1930s by Alonzo Church , is a formal system of computation built from function application . In 1937 Alan Turing proved that the lambda calculus and Turing machines are equivalent models of computation, showing that
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#17327725529131056-434: A higher-order function is the differential operator d / d x {\displaystyle d/dx} , which returns the derivative of a function f {\displaystyle f} . Higher-order functions are closely related to first-class functions in that higher-order functions and first-class functions both allow functions as arguments and results of other functions. The distinction between
1144-468: A language that shares C's block syntax. C-family languages have features like: C-family languages span multiple programming paradigms, conceptual models, and run-time environments. C (programming language) C ( pronounced / ˈ s iː / – like the letter c ) is a general-purpose programming language . It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect
1232-471: A loop to traverse and modify a list. A functional program, on the other hand, would probably use a higher-order "map" function that takes a function and a list, generating and returning a new list by applying the function to each list item. The following two examples (written in JavaScript ) achieve the same effect: they multiply all even numbers in an array by 10 and add them all, storing the final sum in
1320-502: A program's storage requirements, and proposes an operational semantics to aid in such analysis. Harper 2009 proposes including both strict and lazy evaluation in the same language, using the language's type system to distinguish them. Especially since the development of Hindley–Milner type inference in the 1970s, functional programming languages have tended to use typed lambda calculus , rejecting all invalid programs at compilation time and risking false positive errors , as opposed to
1408-411: A program, given appropriate templates and examples, many students find them difficult to understand conceptually, e.g., when asked to define new monads (which is sometimes needed for certain types of libraries). Functional languages also simulate states by passing around immutable states. This can be done by making a function accept the state as one of its parameters, and return a new state together with
1496-633: A role analogous to built-in control structures such as loops in imperative languages . Most general purpose functional programming languages allow unrestricted recursion and are Turing complete , which makes the halting problem undecidable , can cause unsoundness of equational reasoning , and generally requires the introduction of inconsistency into the logic expressed by the language's type system . Some special purpose languages such as Coq allow only well-founded recursion and are strongly normalizing (nonterminating computations can be expressed only with infinite streams of values called codata ). As
1584-590: A semicolon; as a side effect of the evaluation, functions may be called and variables assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if ... [ else ] conditional execution and by do ... while , while , and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. break and continue can be used within
1672-433: A stack and lets the stack overflow . However, when this happens, its garbage collector will claim space back, allowing an unbounded number of active tail calls even though it does not turn tail recursion into a loop. Common patterns of recursion can be abstracted away using higher-order functions, with catamorphisms and anamorphisms (or "folds" and "unfolds") being the most obvious examples. Such recursion schemes play
1760-476: A technique that applies a function to its arguments one at a time, with each application returning a new function that accepts the next argument. This lets a programmer succinctly express, for example, the successor function as the addition operator partially applied to the natural number one. Pure functions (or expressions) have no side effects (memory or I/O). This means that pure functions have several useful properties, many of which can be used to optimize
1848-423: A warning message if a local function was called with the wrong number of arguments, or if different calls to an external function used different numbers or types of arguments. Separate tools such as Unix's lint utility were developed that (among other things) could check for consistency of function use across multiple source files. In the years following the publication of K&R C, several features were added to
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#17327725529131936-612: A wide variety of mainframe computers , minicomputers , and microcomputers , including the IBM PC , as its popularity began to increase significantly. In 1983 the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to
2024-451: Is graph reduction . Lazy evaluation is used by default in several pure functional languages, including Miranda , Clean , and Haskell . Hughes 1984 argues for lazy evaluation as a mechanism for improving program modularity through separation of concerns , by easing independent implementation of producers and consumers of data streams. Launchbury 1993 describes some difficulties that lazy evaluation introduces, particularly in analyzing
2112-476: Is transparent, as it does not implicitly change the input x and thus has no such side effects . Functional programs exclusively use this type of function and are therefore referentially transparent. Purely functional data structures are often represented in a different way to their imperative counterparts. For example, the array with constant access and update times is a basic component of most imperative languages, and many imperative data-structures, such as
2200-623: Is a programming paradigm where programs are constructed by applying and composing functions . It is a declarative programming paradigm in which function definitions are trees of expressions that map values to other values, rather than a sequence of imperative statements which update the running state of the program. In functional programming, functions are treated as first-class citizens , meaning that they can be bound to names (including local identifiers ), passed as arguments , and returned from other functions, just as any other data type can. This allows programs to be written in
2288-468: Is also key to some languages that have found success in specific domains, like JavaScript in the Web, R in statistics, J , K and Q in financial analysis, and XQuery / XSLT for XML . Domain-specific declarative languages like SQL and Lex / Yacc use some elements of functional programming, such as not allowing mutable values . In addition, many other programming languages support programming in
2376-456: Is an informal name for the current major C language standard revision. It was informally known as "C2X" through most of its development. C23 was published in October 2024 as ISO/IEC 9899:2024. The standard macro __STDC_VERSION__ is defined as 202311L to indicate that C23 support is available. C2Y is an informal name for the next major C language standard revision, after C23 (C2X), that
2464-406: Is being evaluated. The technical difference is in the denotational semantics of expressions containing failing or divergent computations. Under strict evaluation, the evaluation of any term containing a failing subterm fails. For example, the expression: fails under strict evaluation because of the division by zero in the third element of the list. Under lazy evaluation, the length function returns
2552-504: Is defined as 201112L to indicate that C11 support is available. C17 is an informal name for ISO/IEC 9899:2018, a standard for the C programming language published in June 2018. It introduces no new language features, only technical corrections, and clarifications to defects in C11. The standard macro __STDC_VERSION__ is defined as 201710L to indicate that C17 support is available. C23
2640-524: Is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC , Solaris Studio , and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++ , however, implements
2728-469: Is hoped to be released later in the 2020s decade, hence the '2' in "C2Y". An early working draft of C2Y was released in February 2024 as N3220 by the working group ISO/IEC JTC1/SC22 /WG14. Historically, embedded C programming requires non-standard extensions to the C language to support exotic features such as fixed-point arithmetic , multiple distinct memory banks , and basic I/O operations. In 2008,
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2816-435: Is not simply an optimization; it is a language feature that assures users that they can use recursion to express a loop and doing so would be safe-for-space. Moreover, contrary to its name, it accounts for all tail calls, not just tail recursion. While proper tail recursion is usually implemented by turning code into imperative loops, implementations might implement it in other ways. For example, Chicken intentionally maintains
2904-622: Is now also referred to as C78 . The second edition of the book covers the later ANSI C standard, described below. K&R introduced several language features: Even after the publication of the 1989 ANSI standard, for many years K&R C was still considered the " lowest common denominator " to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well. In early versions of C, only functions that return types other than int must be declared if used before
2992-420: Is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language. ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22 /WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication. One of
3080-453: Is usually accomplished via recursion . Recursive functions invoke themselves, letting an operation be repeated until it reaches the base case . In general, recursion requires maintaining a stack , which consumes space in a linear amount to the depth of recursion. This could make recursion prohibitively expensive to use instead of imperative loops. However, a special form of recursion known as tail recursion can be recognized and optimized by
3168-724: Is written in Coq and formally verified. A limited form of dependent types called generalized algebraic data types (GADT's) can be implemented in a way that provides some of the benefits of dependently typed programming while avoiding most of its inconvenience. GADT's are available in the Glasgow Haskell Compiler , in OCaml and in Scala , and have been proposed as additions to other languages including Java and C#. Functional programs do not have assignment statements, that is,
3256-461: The Curry–Howard isomorphism , then, well-typed programs in these languages become a means of writing formal mathematical proofs from which a compiler can generate certified code . While these languages are mainly of interest in academic research (including in formalized mathematics ), they have begun to be used in engineering as well. Compcert is a compiler for a subset of the language C that
3344-597: The IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C". This version of the language is often referred to as ANSI C , Standard C, or sometimes C89. In 1990 the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which
3432-899: The OpenSCAD language built on the CGAL framework, although its restriction on reassigning values (all values are treated as constants) has led to confusion among users who are unfamiliar with functional programming as a concept. Functional programming continues to be used in commercial settings. A number of concepts and paradigms are specific to functional programming, and generally foreign to imperative programming (including object-oriented programming ). However, programming languages often cater to several programming paradigms, so programmers using "mostly imperative" languages may have utilized some of these concepts. Higher-order functions are functions that can either take other functions as arguments or return them as results. In calculus, an example of
3520-518: The hash table and binary heap , are based on arrays. Arrays can be replaced by maps or random access lists, which admit purely functional implementation, but have logarithmic access and update times. Purely functional data structures have persistence , a property of keeping previous versions of the data structure unmodified. In Clojure, persistent data structures are used as functional alternatives to their imperative counterparts. Persistent vectors, for example, use trees for partial updating. Calling
3608-505: The lambda calculus , a formal system of computation based only on functions. Functional programming has historically been less popular than imperative programming, but many functional languages are seeing use today in industry and education, including Common Lisp , Scheme , Clojure , Wolfram Language , Racket , Erlang , Elixir , OCaml , Haskell , and F# . Lean is a functional programming language commonly used for verifying mathematical theorems. Functional programming
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3696-596: The principle of compositionality . Backus's paper popularized research into functional programming, though it emphasized function-level programming rather than the lambda-calculus style now associated with functional programming. The 1973 language ML was created by Robin Milner at the University of Edinburgh , and David Turner developed the language SASL at the University of St Andrews . Also in Edinburgh in
3784-601: The untyped lambda calculus , that accepts all valid programs at compilation time and risks false negative errors , used in Lisp and its variants (such as Scheme ), as they reject all invalid programs at runtime when the information is enough to not reject valid programs. The use of algebraic data types makes manipulation of complex data structures convenient; the presence of strong compile-time type checking makes programs more reliable in absence of other reliability techniques like test-driven development , while type inference frees
3872-686: The 1970s, Guy L. Steele and Gerald Jay Sussman developed Scheme , as described in the Lambda Papers and the 1985 textbook Structure and Interpretation of Computer Programs . Scheme was the first dialect of lisp to use lexical scoping and to require tail-call optimization , features that encourage functional programming. In the 1980s, Per Martin-Löf developed intuitionistic type theory (also called constructive type theory), which associated functional programs with constructive proofs expressed as dependent types . This led to new approaches to interactive theorem proving and has influenced
3960-424: The 1970s, Burstall and Darlington developed the functional language NPL . NPL was based on Kleene Recursion Equations and was first introduced in their work on program transformation. Burstall, MacQueen and Sannella then incorporated the polymorphic type checking from ML to produce the language Hope . ML eventually developed into several dialects, the most common of which are now OCaml and Standard ML . In
4048-483: The C Standards Committee published a technical report extending the C language to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as fixed-point arithmetic, named address spaces, and basic I/O hardware addressing. C has a formal grammar specified by the C standard. Line endings are generally not significant in C; however, line boundaries do have significance during
4136-597: The C89 standard and those parts of C99 that are required for compatibility with C++11 . In addition, the C99 standard requires support for identifiers using Unicode in the form of escaped characters (e.g. \u0040 or \U0001f431 ) and suggests support for raw Unicode names. Work began in 2007 on another revision of the C standard, informally called "C1X" until its official publication of ISO/IEC 9899:2011 on December 8, 2011. The C standards committee adopted guidelines to limit
4224-531: The address of the first item in the array. Pass-by-reference is simulated in C by explicitly passing pointers to the thing being referenced. C program source text is free-form code. Semicolons terminate statements , while curly braces are used to group statements into blocks . The C language also exhibits the following characteristics: While C does not include certain features found in other languages (such as object orientation and garbage collection ), these can be implemented or emulated, often through
4312-438: The adoption of new features that had not been tested by existing implementations. The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__
4400-428: The aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features. The standards committee also included several additional features such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales , and preprocessor enhancements. Although the syntax for parameter declarations
4488-416: The basis for several implementations of C on new platforms. In 1978 Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language . Known as K&R from the initials of its authors, the book served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as " K&R C ". As this was released in 1978, it
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#17327725529134576-804: The basis for statically typed functional programming. The first high-level functional programming language, Lisp , was developed in the late 1950s for the IBM 700/7000 series of scientific computers by John McCarthy while at Massachusetts Institute of Technology (MIT). Lisp functions were defined using Church's lambda notation, extended with a label construct to allow recursive functions. Lisp first introduced many paradigmatic features of functional programming, though early Lisps were multi-paradigm languages , and incorporated support for numerous programming styles as new paradigms evolved. Later dialects, such as Scheme and Clojure , and offshoots such as Dylan and Julia , sought to simplify and rationalise Lisp around
4664-418: The capabilities of the targeted CPUs. It has found lasting use in operating systems code (especially in kernels ), device drivers , and protocol stacks , but its use in application software has been decreasing. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems . A successor to the programming language B , C
4752-639: The code: While most compilers for imperative programming languages detect pure functions and perform common-subexpression elimination for pure function calls, they cannot always do this for pre-compiled libraries, which generally do not expose this information, thus preventing optimizations that involve those external functions. Some compilers, such as gcc , add extra keywords for a programmer to explicitly mark external functions as pure, to enable such optimizations. Fortran 95 also lets functions be designated pure . C++11 added constexpr keyword with similar semantics. Iteration (looping) in functional languages
4840-462: The development of subsequent functional programming languages. The lazy functional language, Miranda , developed by David Turner, initially appeared in 1985 and had a strong influence on Haskell . With Miranda being proprietary, Haskell began with a consensus in 1987 to form an open standard for functional programming research; implementation releases have been ongoing as of 1990. More recently it has found use in niches such as parametric CAD in
4928-514: The end of each expression statement, and the entry to and return from each function call. Sequence points also occur during evaluation of expressions containing certain operators ( && , || , ?: and the comma operator ). This permits a high degree of object code optimization by the compiler, but requires C programmers to take more care to obtain reliable results than is needed for other programming languages. Functional programming In computer science , functional programming
5016-650: The features of the more-powerful PDP-11. A significant addition was a character data type. He called this New B (NB). Thompson started to use NB to write the Unix kernel, and his requirements shaped the direction of the language development. Through to 1972, richer types were added to the NB language: NB had arrays of int and char . Pointers, the ability to generate pointers to other types, arrays of all types, and types to be returned from functions were all also added. Arrays within expressions became pointers. A new compiler
5104-477: The function definition; functions used without prior declaration were presumed to return type int . For example: The int type specifiers which are commented out could be omitted in K&;R C, but are required in later standards. Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue
5192-534: The insert method will result in some but not all nodes being created. Functional programming is very different from imperative programming . The most significant differences stem from the fact that functional programming avoids side effects , which are used in imperative programming to implement state and I/O. Pure functional programming completely prevents side-effects and provides referential transparency. Higher-order functions are rarely used in older imperative programming. A traditional imperative program might use
5280-422: The lambda calculus is Turing complete . Lambda calculus forms the basis of all functional programming languages. An equivalent theoretical formulation, combinatory logic , was developed by Moses Schönfinkel and Haskell Curry in the 1920s and 1930s. Church later developed a weaker system, the simply-typed lambda calculus , which extended the lambda calculus by assigning a data type to all terms. This forms
5368-438: The language, supported by compilers from AT&T (in particular PCC ) and some other vendors. These included: The large number of extensions and lack of agreement on a standard library , together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization. During the late 1970s and 1980s, versions of C were implemented for
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#17327725529135456-413: The loop. Break is used to leave the innermost enclosing loop statement and continue is used to skip to its reinitialisation. There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression. Different from many other languages, control-flow will fall through to
5544-411: The next case unless terminated by a break . Expressions can use a variety of built-in operators and may contain function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next " sequence point "; sequence points include
5632-419: The operating system to a PDP-11 . The original PDP-11 version of Unix was also developed in assembly language. Thompson wanted a programming language for developing utilities for the new platform. He first tried writing a Fortran compiler, but he soon gave up the idea and instead created a cut-down version of the recently developed systems programming language called BCPL . The official description of BCPL
5720-567: The original language designer, served for many years as the de facto standard for the language. C has been standardized since 1989 by the American National Standards Institute (ANSI) and, subsequently, jointly by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). C is an imperative procedural language, supporting structured programming , lexical variable scope , and recursion , with
5808-652: The preprocessing phase. Comments may appear either between the delimiters /* and */ , or (since C99) following // until the end of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside string or character literals. C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements . Declarations either define new types using keywords such as struct , union , and enum , or assign types to and perhaps reserve storage for new variables, usually by writing
5896-518: The presence of side effects explicit. Functional programming languages are typically less efficient in their use of CPU and memory than imperative languages such as C and Pascal . This is related to the fact that some mutable data structures like arrays have a very straightforward implementation using present hardware. Flat arrays may be accessed very efficiently with deeply pipelined CPUs, prefetched efficiently through caches (with no complex pointer chasing ), or handled with SIMD instructions. It
5984-495: The programmer from the need to manually declare types to the compiler in most cases. Some research-oriented functional languages such as Coq , Agda , Cayenne , and Epigram are based on intuitionistic type theory , which lets types depend on terms. Such types are called dependent types . These type systems do not have decidable type inference and are difficult to understand and program with. But dependent types can express arbitrary propositions in higher-order logic . Through
6072-408: The recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically different. The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson , incorporating several ideas from colleagues. Eventually, they decided to port
6160-568: The result, leaving the old state unchanged. Impure functional languages usually include a more direct method of managing mutable state. Clojure , for example, uses managed references that can be updated by applying pure functions to the current state. This kind of approach enables mutability while still promoting the use of pure functions as the preferred way to express computations. Alternative methods such as Hoare logic and uniqueness have been developed to track side effects in programs. Some modern research languages use effect systems to make
6248-530: The same result, and cannot be affected by any mutable state or other side effects . This is in contrast with impure procedures , common in imperative programming , which can have side effects (such as modifying the program's state or taking input from a user). Proponents of purely functional programming claim that by restricting side effects, programs can have fewer bugs , be easier to debug and test , and be more suited to formal verification . Functional programming has its roots in academia , evolving from
6336-537: The top four languages in the TIOBE index , a measure of the popularity of programming languages. C is an imperative , procedural language in the ALGOL tradition. It has a static type system . In C, all executable code is contained within subroutines (also called "functions", though not in the sense of functional programming ). Function parameters are passed by value, although arrays are passed as pointers , i.e.
6424-484: The two is subtle: "higher-order" describes a mathematical concept of functions that operate on other functions, while "first-class" is a computer science term for programming language entities that have no restriction on their use (thus first-class functions can appear anywhere in the program that other first-class entities like numbers can, including as arguments to other functions and as their return values). Higher-order functions enable partial application or currying ,
6512-468: The type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ( { and } , sometimes called "curly brackets") to limit the scope of declarations and to act as a single statement for control structures. As an imperative language, C uses statements to specify actions. The most common statement is an expression statement , consisting of an expression to be evaluated, followed by
6600-476: The urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I . Its original version provided only included files and simple string replacements: #include and #define of parameterless macros. Soon after that, it was extended, mostly by Mike Lesk and then by John Reiser, to incorporate macros with arguments and conditional compilation . Unix
6688-715: The use of external libraries (e.g., the GLib Object System or the Boehm garbage collector ). Many later languages have borrowed directly or indirectly from C, including C++ , C# , Unix's C shell , D , Go , Java , JavaScript (including transpilers ), Julia , Limbo , LPC , Objective-C , Perl , PHP , Python , Ruby , Rust , Swift , Verilog and SystemVerilog (hardware description languages). These languages have drawn many of their control structures and other basic features from C. Most of them also express highly similar syntax to C, and they tend to combine
6776-541: The use on a K&R C-based compiler of features available only in Standard C. After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international character sets. The C standard
6864-435: The value 4 (i.e., the number of items in the list), since evaluating it does not attempt to evaluate the terms making up the list. In brief, strict evaluation always fully evaluates function arguments before invoking the function. Lazy evaluation does not evaluate function arguments unless their values are required to evaluate the function call itself. The usual implementation strategy for lazy evaluation in functional languages
6952-406: The value of a variable in a functional program never changes once defined. This eliminates any chances of side effects because any variable can be replaced with its actual value at any point of execution. So, functional programs are referentially transparent. Consider C assignment statement x=x*10 , this changes the value assigned to the variable x . Let us say that the initial value of x
7040-425: The variable "result". Traditional imperative loop: Functional programming with higher-order functions: Sometimes the abstractions offered by functional programming might lead to development of more robust code that avoids certain issues that might arise when building upon large amount of complex, imperative code, such as off-by-one errors (see Greenspun's tenth rule ). There are tasks (for example, maintaining
7128-423: Was 1 , then two consecutive evaluations of the variable x yields 10 and 100 respectively. Clearly, replacing x=x*10 with either 10 or 100 gives a program a different meaning, and so the expression is not referentially transparent. In fact, assignment statements are never referentially transparent. Now, consider another function such as int plusone ( int x ) { return x + 1 ;}
7216-513: Was augmented to include the style used in C++, the K&R interface continued to be permitted, for compatibility with existing source code. C89 is supported by current C compilers, and most modern C code is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on
7304-706: Was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as " C99 ". It has since been amended three times by Technical Corrigenda. C99 introduced several new features, including inline functions , several new data types (including long long int and a complex type to represent complex numbers ), variable-length arrays and flexible array members , improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity ), and support for one-line comments beginning with // , as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers. C99
7392-511: Was not available at the time, and Thompson modified the syntax to be less 'wordy' and similar to a simplified ALGOL known as SMALGOL. He called the result B , describing it as "BCPL semantics with a lot of SMALGOL syntax". Like BCPL, B had a bootstrapping compiler to facilitate porting to new machines. Ultimately, few utilities were written in B because it was too slow and could not take advantage of PDP-11 features such as byte addressability. In 1971 Ritchie started to improve B, to use
7480-628: Was one of the first operating system kernels implemented in a language other than assembly . Earlier instances include the Multics system (which was written in PL/I ) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL ) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as
7568-466: Was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix . It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages, with C compilers available for practically all modern computer architectures and operating systems. The book The C Programming Language , co-authored by
7656-418: Was the primary influence on John Backus 's FP . In the early 1990s, Iverson and Roger Hui created J . In the mid-1990s, Arthur Whitney , who had previously worked with Iverson, created K , which is used commercially in financial industries along with its descendant Q . In the mid-1960s, Peter Landin invented SECD machine , the first abstract machine for a functional programming language, described
7744-530: Was written, and the language was renamed C. The C compiler and some utilities made with it were included in Version 2 Unix , which is also known as Research Unix . At Version 4 Unix , released in November 1973, the Unix kernel was extensively re-implemented in C. By this time, the C language had acquired some powerful features such as struct types. The preprocessor was introduced around 1973 at
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