Computer programming

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If the white bishop (at b3) moves to a2 capturing the black knight, then the black pawn at b1 is programmed to capture the bishop back (indicated by purple color) at a2. Black has just moved (yellow). Example from a chess game. Notation: if B×N then b1×B. Prog one.png
If the white bishop (at b3) moves to a2 capturing the black knight, then the black pawn at b1 is programmed to capture the bishop back (indicated by purple color) at a2. Black has just moved (yellow). Example from a chess game. Notation: if B×N then b1×B.

Computer programming is the process of designing and building an executable computer program for accomplishing a specific computing task. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosen programming language (commonly referred to as coding [1] [2] ). The source code of a program is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate the performance of a task for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, and formal logic.

Executable file that can be run by a computer

In computing, executable code or an executable file or executable program, sometimes simply referred to as an executable or binary, 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.

Computer program sequence of instructions written to perform a specified task with a computer

A computer program is a collection of instructions that performs a specific task when executed by a computer. A computer requires programs to function.

Computing activity requiring, benefiting from, or creating computers

Computing is any activity that uses computers. It includes developing hardware and software, and using computers to manage and process information, communicate and entertain. Computing is a critically important, integral component of modern industrial technology. Major computing disciplines include computer engineering, software engineering, computer science, information systems, and information technology.

Contents

Related programming tasks include testing, debugging, maintaining a program's source code, implementation of build systems, and management of derived artifacts such as machine code of computer programs. These might be considered part of the programming process, but often the term software development is used for this larger process with the term programming, implementation, or coding reserved for the actual writing of source code. Software engineering combines engineering techniques with software development practices.

Software testing is an investigation conducted to provide stakeholders with information about the quality of the software product or service under test. Software testing can also provide an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation. Test techniques include the process of executing a program or application with the intent of finding software bugs, and verifying that the software product is fit for use.

Debugging is the process of finding and resolving defects or problems within a computer program that prevent correct operation of computer software or a system.

In computing, source code is any collection of code, possibly with comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source code. The source code is often transformed by an assembler or compiler into binary machine code understood by the computer. The machine code might then be stored for execution at a later time. Alternatively, source code may be interpreted and thus immediately executed.

History

Ada Lovelace, whose notes added to the end of Luigi Menabrea's paper included the first algorithm designed for processing by an Analytical Engine. She is often recognized as history's first computer programmer. Ada lovelace.jpg
Ada Lovelace, whose notes added to the end of Luigi Menabrea's paper included the first algorithm designed for processing by an Analytical Engine. She is often recognized as history's first computer programmer.

Programmable devices have existed at least as far back as 1206 AD, when the automata of Al-Jazari were programmable, via pegs and cams, to play various rhythms and drum patterns; [3] and the 1801 Jacquard loom could produce entirely different weaves by changing the "program" - a series of pasteboard cards with holes punched in them.

Cam rotating or sliding piece in a mechanical linkage

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating motion in the follower, which is a lever making contact with the cam.

Jacquard loom loom fitted with a Jacquard machine for weaving complex patterned fabrics

The Jacquard machine is a device fitted to a power loom that simplifies the process of manufacturing textiles with such complex patterns as brocade, damask and matelassé. It was invented by Joseph Marie Jacquard in 1804. The loom was controlled by a "chain of cards"; a number of punched cards laced together into a continuous sequence. Multiple rows of holes were punched on each card, with one complete card corresponding to one row of the design. Several such paper cards, generally white in color, can be seen in the images below. Chains, like Bouchon's earlier use of paper tape, allowed sequences of any length to be constructed, not limited by the size of a card.

Card stock paper, thicker and more durable than normal writing or printing paper

Card stock, also called cover stock or pasteboard, is a paper stock that is thicker and more durable than normal writing or printing paper, but thinner and more flexible than other forms of paperboard.

However, the first computer program is generally dated to 1843, when mathematician Ada Lovelace published an algorithm to calculate a sequence of Bernoulli numbers, intended to be carried out by Charles Babbage's Analytical Engine. [4] Women would continue to dominate the field of computer programming until the mid 1960s. [5]

Ada Lovelace English mathematician, computer programming pioneer

Augusta Ada King, Countess of Lovelace was an English mathematician and writer, chiefly known for her work on Charles Babbage's proposed mechanical general-purpose computer, the Analytical Engine. She was the first to recognise that the machine had applications beyond pure calculation, and published the first algorithm intended to be carried out by such a machine. As a result, she is sometimes regarded as the first to recognise the full potential of a "computing machine" and the first computer programmer.

Algorithm an unambiguous specification of how to solve a class of problems

In mathematics and computer science, an algorithm is an unambiguous specification of how to solve a class of problems. Algorithms can perform calculation, data processing, and automated reasoning tasks.

Charles Babbage English mathematician, philosopher, inventor and mechanical engineer who originated the concept of a programmable computer

Charles Babbage was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer.

Data and instructions were once stored on external punched cards, which were kept in order and arranged in program decks. PunchCardDecks.agr.jpg
Data and instructions were once stored on external punched cards, which were kept in order and arranged in program decks.

In the 1880s Herman Hollerith invented the concept of storing data in machine-readable form. [6] Later a control panel (plugboard) added to his 1906 Type I Tabulator allowed it to be programmed for different jobs, and by the late 1940s, unit record equipment such as the IBM 602 and IBM 604, were programmed by control panels in a similar way; as were the first electronic computers. However, with the concept of the stored-program computers introduced in 1949, both programs and data were stored and manipulated in the same way in computer memory.[ citation needed ]

Herman Hollerith American statistician and inventor

Herman Hollerith was an American inventor who developed an electromechanical punched card tabulator to assist in summarizing information and, later, accounting. He was the founder of the Tabulating Machine Company that was amalgamated in 1911 with three other companies to form a fifth company, the Computing-Tabulating-Recording Company, which was renamed IBM in 1924. Hollerith is regarded as one of the seminal figures in the development of data processing. His invention of the punched card tabulating machine marks the beginning of the era of semiautomatic data processing systems, and his concept dominated that landscape for nearly a century.

Plugboard

A plugboard, or control panel, is an array of jacks, or sockets, into which patch cords can be inserted to complete an electrical circuit. Control panels were used to direct the operation of some unit record equipment. Plugboards were used on some cipher machines, and some early computers.

Unit record equipment electromechanical data processing machine

Starting at the end of the nineteenth century, well before the advent of electronic computers, data processing was performed using electromechanical machines called unit record equipment, electric accounting machines (EAM) or tabulating machines. Unit record machines came to be as ubiquitous in industry and government in the first two-thirds of the twentieth century as computers became in the last third. They allowed large volume, sophisticated data-processing tasks to be accomplished before electronic computers were invented and while they were still in their infancy. This data processing was accomplished by processing punched cards through various unit record machines in a carefully choreographed progression. This progression, or flow, from machine to machine was often planned and documented with detailed flowcharts that used standardized symbols for documents and the various machine functions. All but the earliest machines had high-speed mechanical feeders to process cards at rates from around 100 to 2,000 per minute, sensing punched holes with mechanical, electrical, or, later, optical sensors. The operation of many machines was directed by the use of a removable plugboard, control panel, or connection box. Initially all machines were manual or electromechanical. The first use of an electronic component was in 1937 when a photocell was used in a Social Security bill-feed machine. Electronic components were used on other machines beginning in the late 1940s.

Machine code was the language of early programs, written in the instruction set of the particular machine, often in binary notation. Assembly languages were soon developed that let the programmer specify instruction in a text format, (e.g., ADD X, TOTAL), with abbreviations for each operation code and meaningful names for specifying addresses. However, because an assembly language is little more than a different notation for a machine language, any two machines with different instruction sets also have different assembly languages. Kathleen Booth created one of the first Assembly languages in 1950 for various computers at Birkbeck College. [7]

Machine code set of instructions executed directly by a computers central processing unit (CPU)

Machine code is a computer program written in machine language instructions that can be executed directly by a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very specific task, such as a load, a store, a jump, or an ALU operation on one or more units of data in CPU registers or memory.

Assembly language low level programming language

An assemblylanguage, often abbreviated asm, is any low-level programming language in which there is a very strong correspondence between the program's statements and the architecture's machine code instructions.

Wired control panel for an IBM 402 Accounting Machine. IBM402plugboard.Shrigley.wireside.jpg
Wired control panel for an IBM 402 Accounting Machine.

High-level languages allow the programmer to write programs in terms that are syntactically richer, and more capable of abstracting the code, making it targetable to varying machine instruction sets via compilation declarations and heuristics. The first compiler for a programming language was developed by Grace Hopper. [8] When Hopper went to work on UNIVAC in 1949, she brought the idea of using compilers with her. [9] [10] Compilers harness the power of computers to make programming easier [11] by allowing programmers to specify calculations by entering a formula using infix notation (e.g., Y = X*2 + 5*X + 9) for example. FORTRAN, the first widely used high-level language to have a functional implementation which permitted the abstraction of reusable blocks of code, came out in 1957. [12] In 1951 Frances E. Holberton developed the first sort-merge generator which ran on the UNIVAC I. [13] Another woman working at UNIVAC, Adele Mildred Koss, developed a program that was a precursor to report generators. [13] In Russia, Kateryna Yushchenko developed the Address programming language for the MESM in 1955. [14]

The idea for the creation of COBOL started in 1959 when Mary K. Hawes, who worked for Burroughs Corporation, set up a meeting to discuss creating a common business language. [15] She invited six people, including Grace Hopper. [15] Hopper was involved in developing COBOL as a business language and creating "self-documenting" programming. [16] [17] Hopper's contribution to COBOL was based on her programming language, called FLOW-MATIC. [10] In 1961, Jean E. Sammet developed FORMAC and also published Programming Languages: History and Fundamentals which went on to be a standard work on programming languages. [15] [18]

Programs were mostly still entered using punched cards or paper tape. See computer programming in the punch card era. By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into the computers. Frances Holberton created a code to allow keyboard inputs while she worked at UNIVAC. [19] Text editors were developed that allowed changes and corrections to be made much more easily than with punched cards. Sister Mary Kenneth Keller worked on developing the programming language, BASIC which she was a graduate student at Dartmouth in the 1960s. [20] One of the first object-oriented programming languages, Smalltalk, was developed by seven programmers, including Adele Goldberg, in the 1970s. [21] In 1985, Radia Perlman developed the Spinning Tree Protocol in order to route packets of network information efficiently. [22] [23]

Modern programming

Quality requirements

Software development
Core activities
Paradigms and models
Methodologies and frameworks
Supporting disciplines
Practices
Tools
Standards and Bodies of Knowledge
Glossaries

Whatever the approach to development may be, the final program must satisfy some fundamental properties. The following properties are among the most important:

Readability of source code

In computer programming, readability refers to the ease with which a human reader can comprehend the purpose, control flow, and operation of source code. It affects the aspects of quality above, including portability, usability and most importantly maintainability.

Readability is important because programmers spend the majority of their time reading, trying to understand and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and duplicated code. A study [25] found that a few simple readability transformations made code shorter and drastically reduced the time to understand it.

Following a consistent programming style often helps readability. However, readability is more than just programming style. Many factors, having little or nothing to do with the ability of the computer to efficiently compile and execute the code, contribute to readability. [26] Some of these factors include:

The presentation aspects of this (such as indents, line breaks, color highlighting, and so on) are often handled by the source code editor, but the content aspects reflect the programmer's talent and skills.

Various visual programming languages have also been developed with the intent to resolve readability concerns by adopting non-traditional approaches to code structure and display. Integrated development environments (IDEs) aim to integrate all such help. Techniques like Code refactoring can enhance readability.

Algorithmic complexity

The academic field and the engineering practice of computer programming are both largely concerned with discovering and implementing the most efficient algorithms for a given class of problem. For this purpose, algorithms are classified into orders using so-called Big O notation, which expresses resource use, such as execution time or memory consumption, in terms of the size of an input. Expert programmers are familiar with a variety of well-established algorithms and their respective complexities and use this knowledge to choose algorithms that are best suited to the circumstances.

Chess algorithms as an example

"Programming a Computer for Playing Chess" was a 1950 paper that evaluated a "minimax" algorithm that is part of the history of algorithmic complexity; a course on IBM's Deep Blue (chess computer) is part of the computer science curriculum at Stanford University. [27]

Methodologies

The first step in most formal software development processes is requirements analysis, followed by testing to determine value modeling, implementation, and failure elimination (debugging). There exist a lot of differing approaches for each of those tasks. One approach popular for requirements analysis is Use Case analysis. Many programmers use forms of Agile software development where the various stages of formal software development are more integrated together into short cycles that take a few weeks rather than years. There are many approaches to the Software development process.

Popular modeling techniques include Object-Oriented Analysis and Design (OOAD) and Model-Driven Architecture (MDA). The Unified Modeling Language (UML) is a notation used for both the OOAD and MDA.

A similar technique used for database design is Entity-Relationship Modeling (ER Modeling).

Implementation techniques include imperative languages (object-oriented or procedural), functional languages, and logic languages.

Measuring language usage

It is very difficult to determine what are the most popular of modern programming languages. Methods of measuring programming language popularity include: counting the number of job advertisements that mention the language, [28] the number of books sold and courses teaching the language (this overestimates the importance of newer languages), and estimates of the number of existing lines of code written in the language (this underestimates the number of users of business languages such as COBOL).

Some languages are very popular for particular kinds of applications, while some languages are regularly used to write many different kinds of applications. For example, COBOL is still strong in corporate data centers [29] often on large mainframe computers, Fortran in engineering applications, scripting languages in Web development, and C in embedded software. Many applications use a mix of several languages in their construction and use. New languages are generally designed around the syntax of a prior language with new functionality added, (for example C++ adds object-orientation to C, and Java adds memory management and bytecode to C++, but as a result, loses efficiency and the ability for low-level manipulation).

Debugging

The bug from 1947 which is at the origin of a popular (but incorrect) etymology for the common term for a software defect. H96566k.jpg
The bug from 1947 which is at the origin of a popular (but incorrect) etymology for the common term for a software defect.

Debugging is a very important task in the software development process since having defects in a program can have significant consequences for its users. Some languages are more prone to some kinds of faults because their specification does not require compilers to perform as much checking as other languages. Use of a static code analysis tool can help detect some possible problems. Normally the first step in debugging is to attempt to reproduce the problem. This can be a non-trivial task, for example as with parallel processes or some unusual software bugs. Also, specific user environment and usage history can make it difficult to reproduce the problem.

After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. For example, a bug in a compiler can make it crash when parsing some large source file. However, after simplification of the test case, only few lines from the original source file can be sufficient to reproduce the same crash. Such simplification can be done manually, using a divide-and-conquer approach. The programmer will try to remove some parts of original test case and check if the problem still exists. When debugging the problem in a GUI, the programmer can try to skip some user interaction from the original problem description and check if remaining actions are sufficient for bugs to appear.

Debugging is often done with IDEs like Eclipse, Visual Studio, Xcode, Kdevelop, NetBeans and Code::Blocks. Standalone debuggers like GDB are also used, and these often provide less of a visual environment, usually using a command line. Some text editors such as Emacs allow GDB to be invoked through them, to provide a visual environment.

Programming languages

Different programming languages support different styles of programming (called programming paradigms ). The choice of language used is subject to many considerations, such as company policy, suitability to task, availability of third-party packages, or individual preference. Ideally, the programming language best suited for the task at hand will be selected. Trade-offs from this ideal involve finding enough programmers who know the language to build a team, the availability of compilers for that language, and the efficiency with which programs written in a given language execute. Languages form an approximate spectrum from "low-level" to "high-level"; "low-level" languages are typically more machine-oriented and faster to execute, whereas "high-level" languages are more abstract and easier to use but execute less quickly. It is usually easier to code in "high-level" languages than in "low-level" ones.

Allen Downey, in his book How To Think Like A Computer Scientist, writes:

The details look different in different languages, but a few basic instructions appear in just about every language:
  • Input: Gather data from the keyboard, a file, or some other device.
  • Output: Display data on the screen or send data to a file or other device.
  • Arithmetic: Perform basic arithmetical operations like addition and multiplication.
  • Conditional Execution: Check for certain conditions and execute the appropriate sequence of statements.
  • Repetition: Perform some action repeatedly, usually with some variation.

Many computer languages provide a mechanism to call functions provided by shared libraries. Provided the functions in a library follow the appropriate run-time conventions (e.g., method of passing arguments), then these functions may be written in any other language.

Programmers

Computer programmers are those who write computer software. Their jobs usually involve:

See also

Related Research Articles

A compiler is a computer program that transforms computer code written in one programming language into another programming language. Compilers are a type of translator that support digital devices, primarily computers. The name compiler is primarily used for programs that translate source code from a high-level programming language to a lower level language to create an executable program.

COBOL is a compiled English-like computer programming language designed for business use. It is imperative, procedural and, since 2002, object-oriented. COBOL is primarily used in business, finance, and administrative systems for companies and governments. COBOL is still widely used in legacy applications deployed on mainframe computers, such as large-scale batch and transaction processing jobs. But due to its declining popularity and the retirement of experienced COBOL programmers, programs are being migrated to new platforms, rewritten in modern languages or replaced with software packages. Most programming in COBOL is now purely to maintain existing applications.

Integrated development environment software application used to develop software

An integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools, and a debugger. Most of the modern IDEs have intelligent code completion. Some IDEs, such as NetBeans and Eclipse, contain a compiler, interpreter, or both; others, such as SharpDevelop and Lazarus, do not. The boundary between an integrated development environment and other parts of the broader software development environment is not well-defined. Sometimes a version control system, or various tools to simplify the construction of a graphical user interface (GUI), are integrated. Many modern IDEs also have a class browser, an object browser, and a class hierarchy diagram, for use in object-oriented software development.

Programmer person who writes computer software

A programmer, developer, dev, coder, or software engineer is a person who creates computer software. The term computer programmer can refer to a specialist in one area of computers 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 bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and fixing bugs is termed "debugging" and often uses formal techniques or tools to pinpoint bugs, and since the 1950s, some computer systems have been designed to also deter, detect or auto-correct various computer bugs during operations.

Debugger A computer program

A debugger or debugging tool is a computer program that is used to test and debug other programs. The code to be examined might alternatively be running on an instruction set simulator (ISS), a technique that allows great power in its ability to halt when specific conditions are encountered, but which will typically be somewhat slower than executing the code directly on the appropriate processor. Some debuggers offer two modes of operation, full or partial simulation, to limit this impact.

In computer science, program optimization or software optimization is the process of modifying a software system to make some aspect of it work more efficiently or use fewer resources. In general, a computer program may be optimized so that it executes more rapidly, or to make it capable of operating with less memory storage or other resources, or draw less power.

A programming tool or software development tool is a computer program that software developers use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs, that can be combined together to accomplish a task, much as one might use multiple hand tools to fix a physical object. The most basic tools are a source code editor and a compiler or interpreter, which are used ubiquitously and continuously. Other tools are used more or less depending on the language, development methodology, and individual engineer, and are often used for a discrete task, like a debugger or profiler. Tools may be discrete programs, executed separately – often from the command line – or may be parts of a single large program, called an integrated development environment (IDE). In many cases, particularly for simpler use, simple ad hoc techniques are used instead of a tool, such as print debugging instead of using a debugger, manual timing instead of a profiler, or tracking bugs in a text file or spreadsheet instead of a bug tracking system.

In computer science, the term automatic programming identifies a type of computer programming in which some mechanism generates a computer program to allow human programmers to write the code at a higher abstraction level.

Women in computing role of women in computing around the world

Women in computing have shaped the evolution of information technology. They were among the first programmers in the early-20th century, and contributed substantially to the industry. As technology and practices altered, the role of women as programmers has changed, and the recorded history of the field has downplayed their achievements.

LINC is a fourth-generation programming language, used mostly on Unisys computer systems.

The following outline is provided as an overview of and topical guide to computer programming:

Plus is a "Pascal-like" system implementation language from the University of British Columbia (UBC), Canada, based on the SUE system language developed at the University of Toronto, c. 1971.

Software is programmed instructions stored in the memory of stored-program digital computers for execution by the processor. Software is a recent development in human history, and fundamental to the Information Age.

Algorithmic debugging is a debugging technique that compares the results of sub-computations with what the programmer intended. The technique constructs an internal representation of all computations and sub-computations performed during the execution of a buggy program and then asks the programmer about the correctness of such computations. By asking the programmer questions or using a formal specification, the system can identify precisely where in a program a bug is located. Debugging techniques can dramatically reduce the time and effort spent on debugging.

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Sources

Further reading