A computer program (also a software Computer software, or just software, is a general term primarily used for digitally stored data such as computer programs and other kinds of information read and written by computers. Today, this includes data that has not traditionally been associated with computers, such as film, tapes and records. The term was coined in order to contrast to the program, or just a program) is a sequence of instructions In computer science, an instruction is a single operation of a processor defined by an instruction set architecture. In a broader sense, an "instruction" may be any representation of an element of an executable program, such as a bytecode written to perform a specified task for a computer A computer is a programmable machine that receives input, stores and manipulates data//information, and provides output in a useful format.^[1] A computer requires programs to function, typically executing Execution in computer and software engineering is the process by which a computer or a virtual machine carries out the instructions of a computer program. The instructions in the program trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions in the program the program's instructions in a central processor The Central Processing Unit or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed.^[2] The program has an executable Execution in computer and software engineering is the process by which a computer or a virtual machine carries out the instructions of a computer program. The instructions in the program trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions in the program form that the computer can use directly to execute the instructions. The same program in its human-readable source code In computer science, source code is any collection of statements or declarations written in some human-readable computer programming language. Source code is the means most often used by programmers to specify the actions to be performed by a computer form, from which executable In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU. However, in a more general sense, a file containing instructions programs are derived (e.g., compiled A compiler is a computer program that transforms source code written in a programming language (the source language) into another computer language (the target language, often having a binary form known as object code). The most common reason for wanting to transform source code is to create an executable program), enables a programmer A programmer, computer programmer or coder is someone who writes computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist who writes code for many kinds of software. One who practices or professes a formal approach to programming may also be known as a programmer analyst. A to study and develop its algorithms In mathematics, computer science, and related subjects, an 'algorithm' is an effective method for solving a problem expressed as a finite sequence of instructions. Algorithms are used for calculation, data processing, and many other fields.

Computer source code is often written by computer programmers A programmer, computer programmer or coder is someone who writes computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist who writes code for many kinds of software. One who practices or professes a formal approach to programming may also be known as a programmer analyst. A. Source code is written in a programming language A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication that usually follows one of two main paradigms A programming paradigm is a fundamental style of computer programming. Paradigms differ in the concepts and abstractions used to represent the elements of a program (such as objects, functions, variables, constraints, etc.) and the steps that compose a computation (assignment, evaluation, continuations, data flows, etc.): imperative In computer science, imperative programming is a programming paradigm that describes computation in terms of statements that change a program state. In much the same way that imperative mood in natural languages expresses commands to take action, imperative programs define sequences of commands for the computer to perform or declarative In computer science, declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow. Many languages applying this style attempt to minimize or eliminate side effects by describing what the program should accomplish, rather than describing how to go about accomplishing it. This is in programming. Source code may be converted into an executable file In computing, an executable causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains data. Files that contain instructions for an interpreter or CPU or virtual machine may be considered executables, but are more specifically called scripts or bytecode. Executables are also (sometimes called an executable program or a binary) by a compiler A compiler is a computer program that transforms source code written in a programming language (the source language) into another computer language (the target language, often having a binary form known as object code). The most common reason for wanting to transform source code is to create an executable program and later executed by a central processing unit The Central Processing Unit or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed. Alternatively, computer programs may be executed with the aid of an interpreter In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language. An interpreter may be a program that either, or may be embedded In electronics and computing, firmware is a term often used to denote the fixed, usually rather small, programs and data structures that internally control various electronic devices. Typical examples of devices containing firmware range from end-user products such as remote controls or calculators, through computer parts and devices like hard directly into hardware A personal computer is made up of multiple physical components of computer hardware, upon which can be installed an operating system and a multitude of software to perform the operator's desired functions.

Computer programs may be categorized along functional lines: system software System software is computer software designed to operate the computer hardware and to provide and maintain a platform for running application software and application software Application software, also known as applications or apps, is computer software designed to help the user to perform singular or multiple related specific tasks. Examples include Enterprise software, Accounting software, Office suites, Graphics software and media players. Two or more computer programs may run simultaneously on a single computer, a process known as multitasking In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task. Multitasking solves the problem by.

Programming

#include <stdio.h> int main() {

printf("Hello world!\n"); return 0;

Source code of a program written in the C programming language C is a general-purpose computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system

Computer programming Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language. The code may be a modification of an existing source or something completely new. The purpose of programming is to create a program that exhibits a certain is the iterative process of writing or editing source code In computer science, source code is any collection of statements or declarations written in some human-readable computer programming language. Source code is the means most often used by programmers to specify the actions to be performed by a computer. Editing source code involves testing, analyzing, and refining, and sometimes coordinating with other programmers on a jointly developed program. A person who practices this skill is referred to as a computer programmer A programmer, computer programmer or coder is someone who writes computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist who writes code for many kinds of software. One who practices or professes a formal approach to programming may also be known as a programmer analyst. A, software developer or coder. The sometimes lengthy process of computer programming is usually referred to as software development Software development is the act of working to produce/create software. This software could be produced for a variety of purposes - the three most common purposes are to meet specific needs of a specific client/business, to meet a perceived need of some set of potential users , or for personal use (e.g. a scientist may write software to automate a. The term software engineering Software engineering is a profession and field of study dedicated to designing, implementing, and modifying software so that it is of higher quality, more affordable, maintainable, and faster to build. The term software engineering first appeared in the 1968 NATO Software Engineering Conference, and was meant to provoke thought regarding the is becoming popular as the process is seen as an engineering Engineering is the discipline, art and profession of acquiring and applying technical, scientific, and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or invention discipline.

Paradigms

Computer programs can be categorized by the programming language A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication paradigm A programming paradigm is a fundamental style of computer programming. Paradigms differ in the concepts and abstractions used to represent the elements of a program (such as objects, functions, variables, constraints, etc.) and the steps that compose a computation (assignment, evaluation, continuations, data flows, etc.) used to produce them. Two of the main paradigms are imperative In computer science, imperative programming is a programming paradigm that describes computation in terms of statements that change a program state. In much the same way that imperative mood in natural languages expresses commands to take action, imperative programs define sequences of commands for the computer to perform and declarative In computer science, declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow. Many languages applying this style attempt to minimize or eliminate side effects by describing what the program should accomplish, rather than describing how to go about accomplishing it. This is in.

Programs written using an imperative language specify an algorithm In mathematics, computer science, and related subjects, an 'algorithm' is an effective method for solving a problem expressed as a finite sequence of instructions. Algorithms are used for calculation, data processing, and many other fields using declarations, expressions, and statements.^[3] A declaration couples a variable In computer programming, a variable is a facility for storing data. The current value of the variable is the data actually stored in the variable. Depending on the programming language in question, the data stored in the variable can be intentionally altered during the program run, thus causing its value to change, or vary, hence the name. The name to a datatype In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, stating the possible values for that type, the operations that can be done on that type, and the way the values of that type are stored. For example: var x: integer; . An expression yields a value. For example: 2 + 2 yields 4. Finally, a statement might assign an expression to a variable or use the value of a variable to alter the program's control flow In computer science, control flow refers to the order in which the individual statements, instructions, or function calls of an imperative or a declarative program are executed or evaluated. For example: x := 2 + 2; if x = 4 then do_something(); One criticism of imperative languages is the side effect of an assignment statement on a class of variables called non-local variables.^[4]

Programs written using a declarative language specify the properties that have to be met by the output. They do not specify details expressed in terms of the control flow of the executing machine but of the mathematical relations between the declared objects and their properties. Two broad categories of declarative languages are functional languages In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state. Functional programming has its roots in the and logical languages Engineered languages , are constructed languages devised to test or prove some hypothesis about how languages work or might work. There are at least three subcategories, philosophical languages (or ideal languages), logical languages (sometimes abbreviated as loglangs), and experimental languages. Raymond Brown describes engineered languages as &. The principle behind functional languages (like Haskell Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the primary control construct is the function;) is to not allow side effects In computer science, a function or expression is said to have a side effect if, in addition to producing a value, it also modifies some state or has an observable interaction with calling functions or the outside world. For example, a function might modify a global or a static variable, modify one of its arguments, raise an exception, write data, which makes it easier to reason about programs like mathematical functions.^[4] The principle behind logical languages (like Prolog Prolog is a general purpose logic programming language associated with artificial intelligence and computational linguistics) is to define the problem to be solved — the goal — and leave the detailed solution to the Prolog system itself.^[5] The goal is defined by providing a list of subgoals. Then each subgoal is defined by further providing a list of its subgoals, etc. If a path of subgoals fails to find a solution, then that subgoal is backtracked Backtracking is a general algorithm for finding all solutions to some computational problem, that incrementally builds candidates to the solutions, and abandons each partial candidate c ("backtracks") as soon as it determines that c cannot possibly be completed to a valid solution and another path is systematically attempted.

The form in which a program is created may be textual or visual. In a visual language A visual programming language is any programming language that lets users create programs by manipulating program elements graphically rather than by specifying them textually (also known as diagrammatic programming ). A VPL allows programming with visual expressions, spatial arrangements of text and graphic symbols, used either as elements of program, elements are graphically manipulated rather than textually specified.

Compilation or interpretation

A computer program in the form of a human-readable A human-readable medium or human-readable format is a representation of data or information that can be naturally read by humans, computer programming language is called source code In computer science, source code is any collection of statements or declarations written in some human-readable computer programming language. Source code is the means most often used by programmers to specify the actions to be performed by a computer. Source code may be converted into an executable image by a compiler or executed immediately with the aid of an interpreter.

Either compiled or interpreted programs might be executed in a batch process without human interaction, but interpreted programs allow a user to type commands in an interactive session. In this case the programs are the separate commands, whose execution is chained together. When a language is used to give commands to a software application (such as a shell) it is called a scripting language.

Compiled computer programs are commonly referred to as executables, binary images, or simply as binaries — a reference to the binary file format used to store the executable code. Compilers are used to translate source code from a programming language into either object code or machine code. Object code needs further processing to become machine code, and machine code is the Central Processing Unit's native code, ready for execution.

Interpreted computer programs -in a batch or interactive session- are either decoded and then immediately executed or are decoded into some efficient intermediate representation for future execution. BASIC, Perl, and Python are examples of immediately executed computer programs. Alternatively, Java computer programs are compiled ahead of time and stored as a machine independent code called bytecode. Bytecode is then executed upon request by an interpreter called a virtual machine.

The main disadvantage of interpreters is computer programs run slower than if compiled. Interpreting code is slower than running the compiled version because the interpreter must decode each statement each time it is loaded and then perform the desired action. On the other hand, software development may be quicker using an interpreter because testing is immediate when the compilation step is omitted. Another disadvantage of interpreters is the interpreter must be present on the computer at the time the computer program is executed. By contrast, compiled computer programs need not have the compiler present at the time of execution.

No properties of a programming language require it to be exclusively compiled or exclusively interpreted. The categorization usually reflects the most popular method of language execution. For example, BASIC is thought of as an interpreted language and C a compiled language, despite the existence of BASIC compilers and C interpreters. Some systems use Just-in-time compilation (JIT) whereby sections of the source are compiled 'on the fly' and stored for subsequent executions.

Self-modifying programs

A computer program in execution is normally treated as being different from the data the program operates on. However, in some cases this distinction is blurred when a computer program modifies itself. The modified computer program is subsequently executed as part of the same program. Self-modifying code is possible for programs written in Machine code, assembly language, Lisp, C, COBOL, PL/1, Prolog and javascript (the eval feature) among others.

Execution and storage

Typically, computer programs are stored in non-volatile memory until requested either directly or indirectly to be executed by the computer user. Upon such a request, the program is loaded into random access memory, by a computer program called an operating system, where it can be accessed directly by the central processor. The central processor then executes ("runs") the program, instruction by instruction, until termination. A program in execution is called a process.^[6] Termination is either by normal self-termination or by error — software or hardware error.

Embedded programs

Some computer programs are embedded into hardware. A stored-program computer requires an initial computer program stored in its read-only memory to boot. The boot process is to identify and initialize all aspects of the system, from CPU registers to device controllers to memory contents.^[7] Following the initialization process, this initial computer program loads the operating system and sets the program counter to begin normal operations. Independent of the host computer, a hardware device might have embedded firmware to control its operation. Firmware is used when the computer program is rarely or never expected to change, or when the program must not be lost when the power is off.^[8]

Manual programming

Computer programs historically were manually input to the central processor via switches. An instruction was represented by a configuration of on/off settings. After setting the configuration, an execute button was pressed. This process was then repeated. Computer programs also historically were manually input via paper tape or punched cards. After the medium was loaded, the starting address was set via switches and the execute button pressed.^[9]

Automatic program generation

Generative programming is a style of computer programming that creates source code through generic classes, prototypes, , aspects, and code generators to improve programmer productivity. Source code is generated with programming tools such as a or an Integrated Development Environment. The simplest form of source code generator is a macro processor, such as the C preprocessor, which replaces patterns in source code according to relatively simple rules.

Software engines output source code or markup code that simultaneously become the input to another computer process. The analogy is that of one process driving another process, with the computer code being burned as fuel. Application servers are software engines that deliver applications to client computers. For example, a Wiki is an application server that allows users to build dynamic content assembled from articles. Wikis generate HTML, CSS, Java, and Javascript which are then interpreted by a web browser.

Simultaneous execution

Many operating systems support multitasking which enables many computer programs to appear to be running simultaneously on a single computer. Operating systems may run multiple programs through process scheduling — a software mechanism to switch the CPU among processes frequently so that users can interact with each program while it is running.^[10] Within hardware, modern day multiprocessor computers or computers with multicore processors may run multiple programs.^[11]

A single computer program can calculate simultaneously more than one operation using threads or separate processes. Multithreading processors are optimized to execute multiple threads efficiently.

Functional categories

Computer programs may be categorized along functional lines. The main functional categories are system software and application software. System software includes the operating system which couples the computer's hardware with the application software.^[12] The purpose of the operating system is to provide an environment in which application software executes in a convenient and efficient manner.^[12] In addition to the operating system, system software includes utility programs that help manage and tune the computer. If a computer program is not system software then it is application software. Application software includes middleware, which couples the system software with the user interface. Application software also includes utility programs that help users solve application problems, like the need for sorting.

Sometimes development environments for software development are seen as a functional category on its own, specially in the context of Human-Computer Interaction and programming language design. Development environments gather system software (such as compilers and system's batch processing scripting languages) and application software (such as IDEs) with the specific purpose of allowing programmers to create new programs.

See also

• Algorithm for the relationship between computer programs and algorithms.
• Data structure

References

1. ^ Stair, Ralph M., et al. (2003). Principles of Information Systems, Sixth Edition. Thomson Learning, Inc.. pp. 132. ISBN 0-619-06489-7.
2. ^ Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 58. ISBN 0-201-50480-4.
3. ^ Wilson, Leslie B. (1993). Comparative Programming Languages, Second Edition. Addison-Wesley. pp. 75. ISBN 0-201-56885-3.
4. ^ ^{a b} Wilson, Leslie B. (1993). Comparative Programming Languages, Second Edition. Addison-Wesley. pp. 213. ISBN 0-201-56885-3.
5. ^ Wilson, Leslie B. (1993). Comparative Programming Languages, Second Edition. Addison-Wesley. pp. 244. ISBN 0-201-56885-3.
6. ^ Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 97. ISBN 0-201-50480-4.
7. ^ Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 30. ISBN 0-201-50480-4.
8. ^ Tanenbaum, Andrew S. (1990). Structured Computer Organization, Third Edition. Prentice Hall. pp. 11. ISBN 0-13-854662-2.
9. ^ Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 6. ISBN 0-201-50480-4.
10. ^ Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 100. ISBN 0-201-50480-4.
11. ^ Akhter, Shameem (2006). Multi-Core Programming. Richard Bowles (Intel Press). pp. 11–13. ISBN 0-9764832-4-6.
12. ^ ^{a b} Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. pp. 1. ISBN 0-201-50480-4.

Further reading

• Knuth, Donald E. (1997). The Art of Computer Programming, Volume 1, 3rd Edition. Boston: Addison-Wesley. ISBN 0-201-89683-4.
• Knuth, Donald E. (1997). The Art of Computer Programming, Volume 2, 3rd Edition. Boston: Addison-Wesley. ISBN 0-201-89684-2.
• Knuth, Donald E. (1997). The Art of Computer Programming, Volume 3, 3rd Edition. Boston: Addison-Wesley. ISBN 0-201-89685-0.

External links

• Definition of "Program" at Webopedia
• Definition of "Software" at FOLDOC
• Definition of "Computer Program" at dictionary.com

Categories: Computer programming | Computing terminology

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