A computer program, or just a program, is a sequence of instructions, written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor.The program has an executable form that the computer can use directly to execute the instructions. The same program in its human-readable source code form, from which executable programs are derived (e.g., compiled), enables a programmer to study and develop its algorithms. A collection of computer programs and related data is referred to as the software.
Computer source code is typically written by computer programmers. Source code is written in a programming language that usually follows one of two main paradigms: imperative or declarative programming. Source code may be converted into an executable file (sometimes called an executable program or a binary) by a compiler and later executed by a central processing unit. Alternatively, computer programs may be executed with the aid of an interpreter, or may be embedded directly into hardware.
Computer programs may be ranked along functional lines: system software and application software. Two or more computer programs may run simultaneously on one computer from the perspective of the user, this process being known as multitasking.
Computer source code is typically written by computer programmers. Source code is written in a programming language that usually follows one of two main paradigms: imperative or declarative programming. Source code may be converted into an executable file (sometimes called an executable program or a binary) by a compiler and later executed by a central processing unit. Alternatively, computer programs may be executed with the aid of an interpreter, or may be embedded directly into hardware.
Computer programs may be ranked along functional lines: system software and application software. Two or more computer programs may run simultaneously on one computer from the perspective of the user, this process being known as multitasking.
Programming
Computer programming is the iterative process of writing or editing source code. Editing source code involves testing, analyzing, 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, software developer, and sometimes coder.
The sometimes lengthy process of computer programming is usually referred to as software development. The term software engineering is becoming popular as the process is seen as an engineering discipline.
Paradigms
Computer programs can be categorized by the programming language paradigm used to produce them. Two of the main paradigms are imperative and declarative.
Programs written using an imperative language specify an algorithm using declarations, expressions, and statements.[4] A declaration couples a variable name to a datatype. 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. 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.[5]
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 and logical languages. The principle behind functional languages (like Haskell) is to not allow side effects, which makes it easier to reason about programs like mathematical functions.[5] The principle behind logical languages (like Prolog) is to define the problem to be solved — the goal — and leave the detailed solution to the Prolog system itself.[6] 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 and another path is systematically attempted.
The form in which a program is created may be textual or visual. In a visual language program, elements are graphically manipulated rather than textually specified.
Programs written using an imperative language specify an algorithm using declarations, expressions, and statements.[4] A declaration couples a variable name to a datatype. 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. 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.[5]
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 and logical languages. The principle behind functional languages (like Haskell) is to not allow side effects, which makes it easier to reason about programs like mathematical functions.[5] The principle behind logical languages (like Prolog) is to define the problem to be solved — the goal — and leave the detailed solution to the Prolog system itself.[6] 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 and another path is systematically attempted.
The form in which a program is created may be textual or visual. In a visual language program, elements are graphically manipulated rather than textually specified.
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. Termination is either by normal self-termination or by error — software or hardware error.
Automatic program generation
Generative programming is a style of computer programming that creates source code through generic classes, prototypes, templates, aspects, and code generators to improve programmer productivity. Source code is generated with programming tools such as a template processor 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. Application servers are software engines that deliver applications to client computers. For example, a Wiki is an application server that lets users build dynamic content assembled from articles. Wikis generate HTML, CSS, Java, and JavaScript which are then interpreted by a web browser.
Software engines output source code or markup code that simultaneously become the input to another computer process. Application servers are software engines that deliver applications to client computers. For example, a Wiki is an application server that lets users build dynamic content assembled from articles. Wikis generate HTML, CSS, Java, and JavaScript which are then interpreted by a web browser.
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 computer hardware with application software.The purpose of the operating system is to provide an environment in which application software executes in a convenient and efficient manner. 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, especially in the context of human-computer interaction and programming language design.[clarification needed] Development environments gather system software (such as compilers and system's batch processing scripting languages) and application software (such as IDEs) for the specific purpose of helping programmers create new programs.
Sometimes development environments for software development are seen as a functional category on its own, especially in the context of human-computer interaction and programming language design.[clarification needed] Development environments gather system software (such as compilers and system's batch processing scripting languages) and application software (such as IDEs) for the specific purpose of helping programmers create new programs.
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