Computer programming

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Computer programming or coding is the composition of sequences of instructions, called programs, that computers can follow to perform tasks. [1] [2] It involves designing and implementing algorithms, step-by-step specifications of procedures, by writing code in one or more programming languages. Programmers typically use high-level programming languages that are more easily intelligible to humans than machine code, which is directly executed by the central processing unit. Proficient programming usually requires expertise in several different subjects, including knowledge of the application domain, details of programming languages and generic code libraries, specialized algorithms, and formal logic.

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Auxiliary tasks accompanying and related to programming include analyzing requirements, testing, debugging (investigating and fixing problems), implementation of build systems, and management of derived artifacts, such as programs' machine code. While these are sometimes considered programming, often the term software development is used for this larger overall process – with the terms programming, implementation, and coding reserved for the writing and editing of code per se. Sometimes software development is known as software engineering , especially when it employs formal methods or follows an engineering design process.

History

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

Programmable devices have existed for centuries. As early as the 9th century, a programmable music sequencer was invented by the Persian Banu Musa brothers, who described an automated mechanical flute player in the Book of Ingenious Devices . [3] [4] In 1206, the Arab engineer Al-Jazari invented a programmable drum machine where a musical mechanical automaton could be made to play different rhythms and drum patterns, via pegs and cams. [5] [6] In 1801, the Jacquard loom could produce entirely different weaves by changing the "program" – a series of pasteboard cards with holes punched in them.

Code-breaking algorithms have also existed for centuries. In the 9th century, the Arab mathematician Al-Kindi described a cryptographic algorithm for deciphering encrypted code, in A Manuscript on Deciphering Cryptographic Messages. He gave the first description of cryptanalysis by frequency analysis, the earliest code-breaking algorithm. [7]

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. [8] However, Charles Babbage himself had written a program for the AE in 1837. [9] [10]

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. [11] Later a control panel (plug board) 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 computer introduced in 1949, both programs and data were stored and manipulated in the same way in computer memory. [12]

Machine language

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 instructions 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, two machines with different instruction sets also have different assembly languages.

Wired control panel for an IBM 402 Accounting Machine. Wires connect pulse streams from the card reader to counters and other internal logic and ultimately to the printer. IBM402plugboard.Shrigley.wireside.jpg
Wired control panel for an IBM 402 Accounting Machine. Wires connect pulse streams from the card reader to counters and other internal logic and ultimately to the printer.

Compiler languages

High-level languages made the process of developing a program simpler and more understandable, and less bound to the underlying hardware. The first compiler related tool, the A-0 System, was developed in 1952 [13] by Grace Hopper, who also coined the term 'compiler'. [14] [15] FORTRAN, the first widely used high-level language to have a functional implementation, came out in 1957, [16] and many other languages were soon developed—in particular, COBOL aimed at commercial data processing, and Lisp for computer research.

These compiled languages allow the programmer to write programs in terms that are syntactically richer, and more capable of abstracting the code, making it easy to target varying machine instruction sets via compilation declarations and heuristics. Compilers harnessed the power of computers to make programming easier [16] by allowing programmers to specify calculations by entering a formula using infix notation.

Source code entry

Programs were mostly entered using punched cards or paper tape. By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into the computers. Text editors were also developed that allowed changes and corrections to be made much more easily than with punched cards.

Modern programming

Quality requirements

Whatever the approach to development may be, the final program must satisfy some fundamental properties. The following properties are among the most important: [17] [18]

Using automated tests and fitness functions can help to maintain some of the aforementioned attributes. [20]

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, reusing, and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and duplicated code. A study found that a few simple readability transformations made code shorter and drastically reduced the time to understand it. [21]

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. [22] 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 concerned with discovering and implementing the most efficient algorithms for a given class of problems. For this purpose, algorithms are classified into orders using 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.

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 different 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 programming languages.

Measuring language usage

It is very difficult to determine what are the most popular modern programming languages. Methods of measuring programming language popularity include: counting the number of job advertisements that mention the language, [23] 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 [24] 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 first known actual bug causing a problem in a computer was a moth, trapped inside a Harvard mainframe, recorded in a log book entry dated September 9, 1947. "Bug" was already a common term for a software defect when this insect was found. First Computer Bug, 1945.jpg
The first known actual bug causing a problem in a computer was a moth, trapped inside a Harvard mainframe, recorded in a log book entry dated September 9, 1947. "Bug" was already a common term for a software defect when this insect was found.

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, when a bug in a compiler can make it crash when parsing some large source file, a simplification of the test case that results in only few lines from the original source file can be sufficient to reproduce the same crash. Trial-and-error/divide-and-conquer is needed: the programmer will try to remove some parts of the 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 the remaining actions are sufficient for bugs to appear. Scripting and breakpointing are also part of this process.

Debugging is often done with IDEs. 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. Programming languages are essential for software development. They are the building blocks for all software, from the simplest applications to the most sophisticated 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:

Although programming has been presented in the media as a somewhat mathematical subject, some research shows that good programmers have strong skills in natural human languages, and that learning to code is similar to learning a foreign language. [26] [27]

See also

Related Research Articles

<span class="mw-page-title-main">Software</span> Instructions a computer can execute

Software consists of computer programs that instruct the execution of a computer. Software also includes design documents and specifications.

In computing, a compiler is a computer program that translates computer code written in one programming language into another language. The name "compiler" is primarily used for programs that translate source code from a high-level programming language to a low-level programming language to create an executable program.

<span class="mw-page-title-main">Computer program</span> Instructions a computer can execute

.

<span class="mw-page-title-main">Programming language</span> Language for communicating instructions to a machine

A programming language is a system of notation for writing computer programs.

PL/I is a procedural, imperative computer programming language initially developed by IBM. It is designed for scientific, engineering, business and system programming. It has been in continuous use by academic, commercial and industrial organizations since it was introduced in the 1960s.

In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer.

A software bug is a design defect (bug) in computer software. A computer program with many or serious bugs may be described as buggy.

<span class="mw-page-title-main">Debugger</span> Computer program used to test and debug other programs

A debugger or debugging tool is a computer program used to test and debug other programs. The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its execution and monitor changes in computer resources that may indicate malfunctioning code. Typical debugging facilities include the ability to run or halt the target program at specific points, display the contents of memory, CPU registers or storage devices, and modify memory or register contents in order to enter selected test data that might be a cause of faulty program execution.

A disassembler is a computer program that translates machine language into assembly language—the inverse operation to that of an assembler. Disassembly, the output of a disassembler, is often formatted for human-readability rather than suitability for input to an assembler, making it principally a reverse-engineering tool. Common uses of disassemblers include analyzing high-level programming language compilers output and their optimizations, recovering source code of a program whose original source was lost, malware analysis, modifying software, and software cracking.

<span class="mw-page-title-main">Interpreter (computing)</span> Program that executes source code without a separate compilation step

In computer science, an interpreter is a computer program that directly executes instructions written in a programming or scripting language, without requiring them previously to have been compiled into a machine language program. An interpreter generally uses one of the following strategies for program execution:

  1. Parse the source code and perform its behavior directly;
  2. Translate source code into some efficient intermediate representation or object code and immediately execute that;
  3. Explicitly execute stored precompiled bytecode made by a compiler and matched with the interpreter's virtual machine.

In computer science, program optimization, code 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 to accomplish a task, much as one might use multiple hands 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, 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.

Execution in computer and software engineering is the process by which a computer or virtual machine interprets and acts on the instructions of a computer program. Each instruction of a program is a description of a particular action which must be carried out, in order for a specific problem to be solved. Execution involves repeatedly following a "fetch–decode–execute" cycle for each instruction done by the control unit. As the executing machine follows the instructions, specific effects are produced in accordance with the semantics of those instructions.

In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it. The term is a pun on the name of Werner Heisenberg, the physicist who first asserted the observer effect of quantum mechanics, which states that the act of observing a system inevitably alters its state. In electronics, the traditional term is probe effect, where attaching a test probe to a device changes its behavior.

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

A translator or programming language processor is a computer program that converts the programming instructions written in human convenient form into machine language codes that the computers understand and process. It is a generic term that can refer to a compiler, assembler, or interpreter—anything that converts code from one computer language into another. These include translations between high-level and human-readable computer languages such as C++ and Java, intermediate-level languages such as Java bytecode, low-level languages such as the assembly language and machine code, and between similar levels of language on different computing platforms, as well as from any of these to any other of these. Software and hardware represent different levels of abstraction in computing. Software is typically written in high-level programming languages, which are easier for humans to understand and manipulate, while hardware implementations involve low-level descriptions of physical components and their interconnections. Translator computing facilitates the conversion between these abstraction levels. Overall, translator computing plays a crucial role in bridging the gap between software and hardware implementations, enabling developers to leverage the strengths of each platform and optimize performance, power efficiency, and other metrics according to the specific requirements of the application.

In engineering, debugging is the process of finding the root cause, workarounds and possible fixes for bugs.

<span class="mw-page-title-main">Computer architecture</span> Set of rules describing computer system

In computer science and computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, the description may include the instruction set architecture design, microarchitecture design, logic design, and implementation.

<span class="mw-page-title-main">History of software</span> Description of the evolution and development of software throughout history

Software is a set of 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 is fundamental to the Information Age.

This glossary of computer science is a list of definitions of terms and concepts used in computer science, its sub-disciplines, and related fields, including terms relevant to software, data science, and computer programming.

References

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  3. ↑ Koetsier, Teun (2001). "On the prehistory of programmable machines: musical automata, looms, calculators". Mechanism and Machine Theory. 36 (5). Elsevier: 589–603. doi:10.1016/S0094-114X(01)00005-2.
  4. ↑ Kapur, Ajay; Carnegie, Dale; Murphy, Jim; Long, Jason (2017). "Loudspeakers Optional: A history of non-loudspeaker-based electroacoustic music". Organised Sound . 22 (2). Cambridge University Press: 195–205. doi: 10.1017/S1355771817000103 . ISSN   1355-7718.
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  9. ↑ Rojas, R. (2021). "The Computer Programs of Charles Babbage". IEEE Annals of the History of Computing. 43 (1): 6–18. doi:10.1109/MAHC.2020.3045717.
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  14. ↑ Maurice V. Wilkes. 1968. Computers Then and Now. Journal of the Association for Computing Machinery, 15(1):1–7, January. p. 3 (a comment in brackets added by editor), "(I do not think that the term compiler was then [1953] in general use, although it had in fact been introduced by Grace Hopper.)"
  15. ↑ The World's First COBOL Compilers Archived 13 October 2011 at the Wayback Machine
  16. 1 2 Bergstein, Brian (March 20, 2007). "Fortran creator John Backus dies". NBC News. Archived from the original on April 29, 2020. Retrieved April 25, 2010.
  17. ↑ "NIST To Develop Cloud Roadmap". InformationWeek . November 5, 2010. Computing initiative seeks to remove barriers to cloud adoption in security, interoperability, portability and reliability.
  18. ↑ "What is it based on". Computerworld . April 9, 1984. p. 13. Is it based on ... Reliability Portability. Compatibility
  19. ↑ "Programming 101: Tips to become a good programmer - Wisdom Geek". Wisdom Geek. May 19, 2016. Archived from the original on May 23, 2016. Retrieved May 23, 2016.
  20. ↑ Fundamentals of Software Architecture: An Engineering Approach. O'Reilly Media. 2020. ISBN   978-1492043454.
  21. ↑ Elshoff, James L.; Marcotty, Michael (1982). "Improving computer program readability to aid modification". Communications of the ACM. 25 (8): 512–521. doi: 10.1145/358589.358596 . S2CID   30026641.
  22. ↑ Multiple (wiki). "Readability". Docforge. Archived from the original on April 29, 2020. Retrieved January 30, 2010.
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