A computer program is a collection of instructions that performs a specific task when executed by a computer. A computer requires programs to function, and typically executes the program's instructions in a central processing unit.
A computer program is usually written by a computer programmer in a programming language. From the program in its human-readable form of source code, a compiler can derive machine code—a form consisting of instructions that the computer can directly execute. Alternatively, a computer program may be executed with the aid of an interpreter.
A part of a computer program that performs a well-defined task is known as an algorithm. A collection of computer programs, libraries and related data are referred to as software. Computer programs may be categorized along functional lines, such as application software or system software.
The earliest programmable machines preceded the invention of the digital computer. In 1801, Joseph-Marie Jacquard devised a loom that would weave a pattern by following a series of perforated cards. Patterns could be weaved and repeated by arranging the cards.
In 1837, Charles Babbage was inspired by Jacquard's loom to attempt to build the Analytical Engine. The names of the components of the calculating device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled. The device would have had a "store"—memory to hold 1,000 numbers of 40 decimal digits each. Numbers from the "store" would then have then been transferred to the "mill" (analogous to the CPU of a modern machine), for processing. It was programmed using two sets of perforated cards—one to direct the operation and the other for the input variables. However, after more than 17,000 pounds of the British government's money, the thousands of cogged wheels and gears never fully worked together.
- 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
- 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();
- The word app came to being in 21st century. It is a clipping of the word "application". They have been designed for many platforms, but the word was first used for smaller mobile apps. Desktop apps are traditional computer programs that run on desktop computers. Mobile apps run on mobile devices. Web apps run inside a web browser. Both mobile and desktop apps may be downloaded from the developers' website or purchased from app stores such as Windows Store, Apple App Store, Mac App Store, Google Play or Intel AppUp.
- An application suite consists of multiple applications bundled together. Examples include Microsoft Office, LibreOffice and iWork. They bundle a word processor, spreadsheet, and other applications.
- Enterprise applications bundle accounting, personnel, customer, and vendor applications. Examples include enterprise resource planning, customer relationship management, and supply chain management software.
- Enterprise infrastructure software supports the enterprise's software systems. Examples include databases, email servers, and network servers.
- Information worker software are designed for workers at the departmental level. Examples include time management, resource management, analytical, collaborative and documentation tools. Word processors, spreadsheets, email and blog clients, personal information system, and individual media editors may aid in multiple information worker tasks.
- Media development software generates print and electronic media for others to consume, most often in a commercial or educational setting. These produce graphics, publications, animations, and videos.
- Product engineering software is used to help develop large machines and other application software. Examples includes computer-aided design (CAD), computer-aided engineering (CAE), and integrated development environments.
- Entertainment Software can refer to video games, movie recorders and players, and music recorders and players.
- Knuth, Donald E. (1997). The Art of Computer Programming, Volume 1, 3rd Edition. Boston: Addison-Wesley. ISBN .
- Knuth, Donald E. (1997). The Art of Computer Programming, Volume 2, 3rd Edition. Boston: Addison-Wesley. ISBN .
- Knuth, Donald E. (1997). The Art of Computer Programming, Volume 3, 3rd Edition. Boston: Addison-Wesley. ISBN .
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