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Several separate standard headers for example, stdio. Pass-by-reference is simulated in C by explicitly passing values. July 2014 A number of tools have been developed to help C programmers find and fix statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided by the compiler. The C compiler in , however, implements the C89 standard and those parts of C99 that are required for compatibility with.

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I/C

For the book, see. C , as in the is a , computer , supporting , and , while a prevents many unintended operations. By design, C provides constructs that map efficiently to typical , and therefore it has found lasting use in applications that had formerly been coded in , including , as well as various for computers ranging from to. It has since become one of the of all time, with C from various vendors available for the majority of existing and operating systems. C has been standardized by the ANSI since 1989 see and subsequently by the ISO. C is an language. It was designed to be compiled using a relatively straightforward , to provide access to , to provide language constructs that map efficiently to , and to require minimal. Despite its low-level capabilities, the language was designed to encourage programming. A -compliant C program that is written with in mind can be compiled for a very wide variety of computer platforms and operating systems with few changes to its source code. The language has become available on a very wide range of platforms, from embedded to. Pass-by-reference is simulated in C by explicitly passing values. C program source text is , using the as a terminator and for grouping. User-defined names are not distinguished from keywords by any kind of. Unlike structs, arrays are not first-class objects; they cannot be assigned or compared using single built-in operators. They are freely interconvertible with integers. While C does not include some features found in some other languages, such as or , such features can be implemented or emulated in C, often by way of external libraries e. Relations to other languages Many later languages have borrowed directly or indirectly from C, including , , Unix's , , , , , , , , , , , , , and hardware description languages. These languages have drawn many of their and other basic features from C. Most of them with Python being the most dramatic exception are also very similar to C in general, and they tend to combine the recognizable expression and statement with underlying type systems, data models, and semantics that can be radically different. Eventually, they decided to port the operating system to a. The original PDP-11 version of Unix was developed in assembly language. The developers were considering rewriting the system using the , Thompson's simplified version of. However B's inability to take advantage of some of the PDP-11's features, notably addressability, led to C. The name of C was chosen simply as the next after B. The development of C started in 1972 on the PDP-11 Unix system and first appeared in. The language was not initially designed with portability in mind, but soon ran on different platforms as well: a compiler for the was written within the first year of C's history, while an port followed soon. Also in 1972, a large part of Unix was rewritten in C. By 1973, with the addition of struct types, the C language had become powerful enough that most of the was now in C. Unix was one of the first operating system kernels implemented in a language other than. Earlier instances include the system which was written in and MCP for the which was written in in 1961. In around 1977, Ritchie and made further changes to the language to facilitate portability of the Unix operating system. Johnson's served as the basis for several implementations of C on new platforms. The second edition of the book covers the later standard, described below. In early versions of C, only functions that return types other than int must be declared if used before the function definition; functions used without prior declaration were presumed to return type int. Separate tools such as Unix's utility were developed that among other things could check for consistency of function use across multiple source files. ANSI C and ISO C Main article: During the late 1970s and 1980s, versions of C were implemented for a wide variety of , , and , including the , as its popularity began to increase significantly. In 1983, the 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 the 1003 to become the basis for the 1988 standard. In 1989, the C standard was ratified as ANSI X3. This version of the language is often referred to as , Standard C, or sometimes C89. National adoption of an update to the international standard typically occurs within a year of ISO publication. The standards committee also included several additional features such as borrowed from C++ , void pointers, support for international and , and preprocessor enhancements. C89 is supported by current C compilers, and most C code being written today is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte. It has since been amended three times by Technical Corrigenda. Many of these had already been implemented as extensions in several C compilers. C99 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. The C compiler in , however, implements the C89 standard and those parts of C99 that are required for compatibility with. The C standards committee adopted guidelines to limit 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++. In 2008, the C Standards Committee published a extending the C language to address these issues by providing a common standard for all implementations to adhere to. Main article: C has a specified by the C standard. Line endings are generally not significant in C; however, line boundaries do have significance during the preprocessing phase. C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and. 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 the type followed by the variable name. Keywords such as char and int specify built-in types. 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 a semicolon; as a side effect of the evaluation, functions may be and variables may be new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. There is also a non-structured statement which branches directly to the designated within the function. 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. 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. Some of the operators have the wrong precedence; some parts of the syntax could be better. Additional multi-byte encoded characters may be used in string literals, but they are not entirely. The basic C execution character set contains the same characters, along with representations for , , and. Since existing program source code should not have been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers do define more convenient synonyms for underscored identifiers. The language previously included a reserved word called entry, but this was seldom implemented, and has now been removed as a reserved word. Operators Main article: C supports a rich set of , which are symbols used within an to specify the manipulations to be performed while evaluating that expression. The similarity between these two operators assignment and equality may result in the accidental use of one in place of the other, and in many cases, the mistake does not produce an error message although some compilers produce warnings. The C is not always intuitive. This causes the compiler to replace that line with the entire text of the standard header, which contains declarations for standard input and output functions such as printf. The angle brackets surrounding stdio. The next line indicates that a function named main is being defined. The function serves a special purpose in C programs; the run-time environment calls the main function to begin program execution. The type specifier int indicates that the value that is returned to the invoker in this case the run-time environment as a result of evaluating the main function, is an integer. The keyword void as a parameter list indicates that this function takes no arguments. The opening curly brace indicates the beginning of the definition of the main function. The next line calls diverts execution to a function named , which in this case is supplied from a system. The string literal is an unnamed with elements of type char, set up automatically by the compiler with a final 0-valued character to mark the end of the array printf needs to know this. The return value of the printf function is of type int, but it is silently discarded since it is not used. A more careful program might test the return value to determine whether or not the printf function succeeded. The semicolon ; terminates the statement. The closing curly brace indicates the end of the code for the main function. According to the C99 specification and newer, the main function, unlike any other function, will implicitly return a value of 0 upon reaching the } that terminates the function. Formerly an explicit return 0; statement was required. This is interpreted by the run-time system as an exit code indicating successful execution. This section needs additional citations for. Unsourced material may be challenged and removed. October 2012 The in C is and , which makes it similar to the type system of descendants such as. There are built-in types for integers of various sizes, both signed and unsigned, , and enumerated types enum. Integer type char is often used for single-byte characters. There are also derived types including , , , and union. C is often used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type correctness of most expressions, but the programmer can override the checks in various ways, either by using a to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way. Some find C's declaration syntax unintuitive, particularly for. C's usual arithmetic conversions allow for efficient code to be generated, but can sometimes produce unexpected results. For example, a comparison of signed and unsigned integers of equal width requires a conversion of the signed value to unsigned. This can generate unexpected results if the signed value is negative. Pointers C supports the use of , a type of that records the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or. The run-time representation of a pointer value is typically a raw memory address perhaps augmented by an offset-within-word field , but since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Many data types, such as , are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to such as or or as to be invoked by event handlers. A value explicitly points to no valid location. Dereferencing a null pointer value is undefined, often resulting in a. In appropriate contexts in source code, such as for assigning to a pointer variable, a null pointer constant can be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined by several standard headers. In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be and in many contexts implicitly are converted to and from any other object pointer type. Careless use of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be made to point to any arbitrary location, which can cause undesirable effects. Although properly used pointers point to safe places, they can be made to point to unsafe places by using invalid ; the objects they point to may continue to be used after deallocation ; they may be used without having been initialized ; or they may be directly assigned an unsafe value using a cast, union, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more restrictive types. Arrays See also: types in C are traditionally of a fixed, static size specified at compile time. The more recent C99 standard also allows a form of variable-length arrays. However, it is also possible to allocate a block of memory of arbitrary size at run-time, using the standard library's malloc function, and treat it as an array. C's unification of arrays and pointers means that declared arrays and these dynamically allocated simulated arrays are virtually interchangeable. Since arrays are always accessed in effect via pointers, array accesses are typically not checked against the underlying array size, although some compilers may provide as an option. Array bounds violations are therefore possible and rather common in carelessly written code, and can lead to various repercussions, including illegal memory accesses, corruption of data, , and run-time exceptions. If bounds checking is desired, it must be done manually. C does not have a special provision for declaring , but rather relies on within the type system to declare arrays of arrays, which effectively accomplishes the same thing. Multi-dimensional arrays are commonly used in numerical algorithms mainly from applied to store matrices. The structure of the C array is well suited to this particular task. However, since arrays are passed merely as pointers, the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is not the base address pointed to by x incremented by i bytes, but rather is defined to be the base address incremented by i multiplied by the size of an element that x points to. Furthermore, in most expression contexts a notable exception is as operand of , the name of an array is automatically converted to a pointer to the array's first element. This implies that an array is never copied as a whole when named as an argument to a function, but rather only the address of its first element is passed. Therefore, although function calls in C use semantics, arrays are in effect passed by. Since array name arguments to sizeof are not converted to pointers, they do not exhibit such ambiguity. However, arrays created by dynamic allocation are accessed by pointers rather than true array variables, so they suffer from the same sizeof issues as array pointers. Thus, despite this apparent equivalence between array and pointer variables, there is still a distinction to be made between them. Even though the name of an array is, in most expression contexts, converted into a pointer to its first element , this pointer does not itself occupy any storage; the array name is not an , and its address is a constant, unlike a pointer variable. Array contents may be copied, however, by using the memcpy function, or by accessing the individual elements. One of the most important functions of a programming language is to provide facilities for managing and the objects that are stored in memory. For example, static memory allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a great deal of overhead for both allocation and deallocation. The persistent nature of static objects is useful for maintaining state information across function calls, automatic allocation is easy to use but stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allocation allows convenient allocation of objects whose size is known only at run-time. Most C programs make extensive use of all three. Where possible, automatic or static allocation is usually simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. However, many data structures can change in size at runtime, and since static allocations and automatic allocations before C99 must have a fixed size at compile-time, there are many situations in which dynamic allocation is necessary. Prior to the C99 standard, variable-sized arrays were a common example of this. See the article on for an example of dynamically allocated arrays. Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication in the form of a null pointer value when the required storage cannot be allocated. Static allocation that is too large is usually detected by the or , before the program can even begin execution. Unless otherwise specified, static objects contain zero or null pointer values upon program startup. Automatically and dynamically allocated objects are initialized only if an initial value is explicitly specified; otherwise they initially have indeterminate values typically, whatever happens to be present in the , which might not even represent a valid value for that type. If the program attempts to access an uninitialized value, the results are undefined. Many modern compilers try to detect and warn about this problem, but both can occur. Another issue is that heap memory allocation has to be synchronized with its actual usage in any program in order for it to be reused as much as possible. For example, if the only pointer to a heap memory allocation goes out of scope or has its value overwritten before is called, then that memory cannot be recovered for later reuse and is essentially lost to the program, a phenomenon known as a. Conversely, it is possible for memory to be freed but continue to be referenced, leading to unpredictable results. Typically, the symptoms will appear in a portion of the program far removed from the actual error, making it difficult to track down the problem. Such issues are ameliorated in languages with. The C programming language uses as its primary method of extension. Each library typically has a , which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a program to use a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires e. The most common C library is the , which is specified by the and standards and comes with every C implementation implementations which target limited environments such as may provide only a subset of the standard library. This library supports stream input and output, memory allocation, mathematics, character strings, and time values. Several separate standard headers for example, stdio. Another common set of C library functions are those used by applications specifically targeted for and systems, especially functions which provide an interface to the. These functions are detailed in various standards such as and the. Since many programs have been written in C, there are a wide variety of other libraries available. Libraries are often written in C because C compilers generate efficient ; programmers then create interfaces to the library so that the routines can be used from higher-level languages like , , and. This section needs additional citations for. Unsourced material may be challenged and removed. July 2014 A number of tools have been developed to help C programmers find and fix statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided by the compiler. The tool was the first such, leading to many others. Automated source code checking and auditing are beneficial in any language, and for C many such tools exist, such as. A common practice is to use Lint to detect questionable code when a program is first written. Once a program passes Lint, it is then compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to actually be errors. There are also compilers, libraries, and operating system level mechanisms for performing actions that are not a standard part of C, such as for arrays, detection of , , tracking, and. Tools such as or and linking with libraries containing special versions of the can help uncover runtime errors in memory usage. The graph, showing a comparison of the popularity of various programming languages C is widely used for in implementing and applications, because C code, when written for portability, can be used for most purposes, yet when needed, system-specific code can be used to access specific hardware addresses and to perform to match externally imposed interface requirements, with a low demand on system resources. C is often chosen over because of its speed, stability, and near-universal availability. One consequence of C's wide availability and efficiency is that , libraries and of other programming languages are often implemented in C. The of , and , for example, are all written in C. Because the layer of abstraction is thin and the overhead is low, C enables programmers to create efficient implementations of algorithms and data structures, useful for computationally intense programs. For example, the , the , , and are completely or partially written in C. C is sometimes used as an by implementations of other languages. This approach may be used for portability or convenience; by using C as an intermediate language, additional machine-specific code generators are not necessary. C has some features, such as line-number preprocessor directives and optional superfluous commas at the end of initializer lists, that support compilation of generated code. However, some of C's shortcomings have prompted the development of other specifically designed for use as intermediate languages, such as. C has also been widely used to implement applications. However, such applications can also be written in newer, higher-level languages. C has both directly and indirectly influenced many later languages such as , , , , , , , , , , and Unix's. Several C or near-C interpreters exist, including and , which can also be used for scripting. When object-oriented languages became popular, and were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as ; source code was translated into C, and then compiled with a C compiler. The programming language was devised by as an approach to providing functionality with a C-like syntax. C++ adds greater typing strength, scoping, and other tools useful in object-oriented programming, and permits via templates. Nearly a superset of C, C++ now supports most of C, with. Objective-C derives its syntax from both C and : syntax that involves preprocessing, expressions, function declarations, and function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk. In addition to and , , and are nearly supersets of C. In fact, C99 requires that a diagnostic message be produced. The ISO C standard section 5. Regarded by many to be the authoritative reference on C. The Research School of Computer Science at the Australian National University. Archived from PDF on 2013-11-06. Retrieved 18 July 2006. Archived from on 13 December 2007. Retrieved 16 January 2009. Retrieved 6 May 2009. Retrieved 16 December 2012. International Organization for Standardization. Retrieved 2 June 2011. Retrieved September 7, 2013. Retrieved 26 July 2011. C: A Reference Manual 5th ed. Contains a grammar for C. The C Programming Language 2nd ed. The C Programming Language 2nd ed. Retrieved 26 June 2009. Otsego, MI: PageFree Publishing Inc. Retrieved 10 February 2012. Bangkok, Thailand: SE-EDUCATION PUBLIC COMPANY LIMITED. Retrieved 5 August 2012. Retrieved March 6, 2013. Retrieved March 6, 2013. Retrieved 4 January 2010. Retrieved 9 June 2011.

Certain Zacks Rank stocks for which no month-end price was available, pricing information was not collected, or for certain other reasons have been excluded from these return calculations. C# dictionary check if key exists return value of the printf function is of type int, but it is silently discarded since it is not used. The name of C was chosen simply as the next after B. Several C or near-C interpreters exist, including andwhich can also be used for scripting. The ever popular one-page Snapshot reports are generated for virtually every single Zacks Ranked stock. Prior to the C99 standard, variable-sized arrays were a common example of this. Since existing program source code should not have been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. The Old English 'cw' was also at length displaced by the French 'qu' so that the Old English cwén 'queen' and cwic 'quick' became 'quen' 'quik', respectively. As an investor, you want to buy stocks with the highest probability of success.