Computer programming

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Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Computer programming_sentence_0

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). Computer programming_sentence_1

The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. Computer programming_sentence_2

The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an operating system) on a computer, often for solving a given problem. Computer programming_sentence_3

Proficient programming thus often requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, and formal logic. Computer programming_sentence_4

Tasks accompanying and related to programming include: testing, debugging, source code maintenance, implementation of build systems, and management of derived artifacts, such as the machine code of computer programs. Computer programming_sentence_5

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 code. Computer programming_sentence_6

Software engineering combines engineering techniques with software development practices. Computer programming_sentence_7

Reverse engineering is a related process used by designers, analysts and programmers to understand and re-create/re-implement. Computer programming_sentence_8

History Computer programming_section_0

See also: Computer program § History, Programmer § History, and History of programming languages Computer programming_sentence_9

Programmable devices have existed for centuries. Computer programming_sentence_10

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. Computer programming_sentence_11

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. Computer programming_sentence_12

In 1801, the Jacquard loom could produce entirely different weaves by changing the "program" – a series of pasteboard cards with holes punched in them. Computer programming_sentence_13

Code-breaking algorithms have also existed for centuries. Computer programming_sentence_14

In the 9th century, the Arab mathematician Al-Kindi described a cryptographic algorithm for deciphering encrypted code, in A Manuscript on Deciphering Cryptographic Messages. Computer programming_sentence_15

He gave the first description of cryptanalysis by frequency analysis, the earliest code-breaking algorithm. Computer programming_sentence_16

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. Computer programming_sentence_17

In the 1880s Herman Hollerith invented the concept of storing data in machine-readable form. Computer programming_sentence_18

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. Computer programming_sentence_19

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. Computer programming_sentence_20

Machine language Computer programming_section_1

Machine code was the language of early programs, written in the instruction set of the particular machine, often in binary notation. Computer programming_sentence_21

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. Computer programming_sentence_22

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. Computer programming_sentence_23

Compiler languages Computer programming_section_2

High-level languages made the process of developing a program simpler and more understandable, and less bound to the underlying hardware. Computer programming_sentence_24

FORTRAN, the first widely used high-level language to have a functional implementation, came out in 1957 and many other languages were soon developed – in particular, COBOL aimed at commercial data processing, and Lisp for computer research. Computer programming_sentence_25

These compiled 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. Computer programming_sentence_26

The first compiler for a programming language was developed by Grace Hopper. Computer programming_sentence_27

When Hopper went to work on UNIVAC in 1949, she brought the idea of using compilers with her. Computer programming_sentence_28

Compilers harness the power of computers to make programming easier by allowing programmers to specify calculations by entering a formula using infix notation (e.g., Y = X*2 + 5*X + 9) for example. Computer programming_sentence_29

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 and many other languages were soon developed - in particular, COBOL aimed at commercial data processing, and Lisp for computer research. Computer programming_sentence_30

In 1951 Frances E. Holberton developed the first sort-merge generator, which ran on the UNIVAC I. Computer programming_sentence_31

Another woman working at UNIVAC, Adele Mildred Koss, developed a program that was a precursor to report generators. Computer programming_sentence_32

The idea for the creation of COBOL started in 1959 when Mary K. Hawes, who worked for the Burroughs Corporation, set up a meeting to discuss creating a common business language. Computer programming_sentence_33

She invited six people, including Grace Hopper. Computer programming_sentence_34

Hopper was involved in developing COBOL as a business language and creating "self-documenting" programming. Computer programming_sentence_35

Hopper's contribution to COBOL was based on her programming language, called FLOW-MATIC. Computer programming_sentence_36

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. Computer programming_sentence_37

Source code entry Computer programming_section_3

Programs were mostly still entered using punched cards or paper tape. Computer programming_sentence_38

See Computer programming in the punch card era. Computer programming_sentence_39

By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into the computers. Computer programming_sentence_40

Frances Holberton created a code to allow keyboard inputs while she worked at UNIVAC. Computer programming_sentence_41

Text editors were developed that allowed changes and corrections to be made much more easily than with punched cards. Computer programming_sentence_42

Sister Mary Kenneth Keller worked on developing the programming language BASIC while she was a graduate student at Dartmouth in the 1960s. Computer programming_sentence_43

One of the first object-oriented programming languages, Smalltalk, was developed by seven programmers, including Adele Goldberg, in the 1970s. Computer programming_sentence_44

In 1985, Radia Perlman developed the Spanning Tree Protocol in order to route packets of network information efficiently. Computer programming_sentence_45

Modern programming Computer programming_section_4

Quality requirements Computer programming_section_5

Whatever the approach to development may be, the final program must satisfy some fundamental properties. Computer programming_sentence_46

The following properties are among the most important: Computer programming_sentence_47

Computer programming_unordered_list_0

  • Reliability: how often the results of a program are correct. This depends on conceptual correctness of algorithms, and minimization of programming mistakes, such as mistakes in resource management (e.g., buffer overflows and race conditions) and logic errors (such as division by zero or off-by-one errors).Computer programming_item_0_0
  • Robustness: how well a program anticipates problems due to errors (not bugs). This includes situations such as incorrect, inappropriate or corrupt data, unavailability of needed resources such as memory, operating system services, and network connections, user error, and unexpected power outages.Computer programming_item_0_1
  • Usability: the ergonomics of a program: the ease with which a person can use the program for its intended purpose or in some cases even unanticipated purposes. Such issues can make or break its success even regardless of other issues. This involves a wide range of textual, graphical, and sometimes hardware elements that improve the clarity, intuitiveness, cohesiveness and completeness of a program's user interface.Computer programming_item_0_2
  • Portability: the range of computer hardware and operating system platforms on which the source code of a program can be compiled/interpreted and run. This depends on differences in the programming facilities provided by the different platforms, including hardware and operating system resources, expected behavior of the hardware and operating system, and availability of platform-specific compilers (and sometimes libraries) for the language of the source code.Computer programming_item_0_3
  • Maintainability: the ease with which a program can be modified by its present or future developers in order to make improvements or customizations, fix bugs and security holes, or adapt it to new environments. Good practices during initial development make the difference in this regard. This quality may not be directly apparent to the end user but it can significantly affect the fate of a program over the long term.Computer programming_item_0_4
  • Efficiency/performance: Measure of system resources a program consumes (processor time, memory space, slow devices such as disks, network bandwidth and to some extent even user interaction): the less, the better. This also includes careful management of resources, for example cleaning up and eliminating memory leaks. This is often discussed under the shadow of a chosen programming language. Although the language certainly affects performance, even slower languages, such as Python, can execute programs instantly from a human perspective. Speed, resource usage, and performance are important for programs that bottleneck the system, but efficient use of programmer time is also important and is related to cost: more hardware may be cheaper.Computer programming_item_0_5

Readability of source code Computer programming_section_6

In computer programming, readability refers to the ease with which a human reader can comprehend the purpose, control flow, and operation of source code. Computer programming_sentence_48

It affects the aspects of quality above, including portability, usability and most importantly maintainability. Computer programming_sentence_49

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. Computer programming_sentence_50

Unreadable code often leads to bugs, inefficiencies, and duplicated code. Computer programming_sentence_51

A study found that a few simple readability transformations made code shorter and drastically reduced the time to understand it. Computer programming_sentence_52

Following a consistent programming style often helps readability. Computer programming_sentence_53

However, readability is more than just programming style. Computer programming_sentence_54

Many factors, having little or nothing to do with the ability of the computer to efficiently compile and execute the code, contribute to readability. Computer programming_sentence_55

Some of these factors include: Computer programming_sentence_56

Computer programming_unordered_list_1

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. Computer programming_sentence_57

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. Computer programming_sentence_58

Integrated development environments (IDEs) aim to integrate all such help. Computer programming_sentence_59

Techniques like Code refactoring can enhance readability. Computer programming_sentence_60

Algorithmic complexity Computer programming_section_7

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. Computer programming_sentence_61

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. Computer programming_sentence_62

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. Computer programming_sentence_63

Chess algorithms as an example Computer programming_section_8

"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. Computer programming_sentence_64

Methodologies Computer programming_section_9

The first step in most formal software development processes is requirements analysis, followed by testing to determine value modeling, implementation, and failure elimination (debugging). Computer programming_sentence_65

There exist a lot of differing approaches for each of those tasks. Computer programming_sentence_66

One approach popular for requirements analysis is Use Case analysis. Computer programming_sentence_67

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. Computer programming_sentence_68

There are many approaches to the Software development process. Computer programming_sentence_69

Popular modeling techniques include Object-Oriented Analysis and Design (OOAD) and Model-Driven Architecture (MDA). Computer programming_sentence_70

The Unified Modeling Language (UML) is a notation used for both the OOAD and MDA. Computer programming_sentence_71

A similar technique used for database design is Entity-Relationship Modeling (ER Modeling). Computer programming_sentence_72

Implementation techniques include imperative languages (object-oriented or procedural), functional languages, and logic languages. Computer programming_sentence_73

Measuring language usage Computer programming_section_10

Main article: Measuring programming language popularity Computer programming_sentence_74

It is very difficult to determine what are the most popular modern programming languages. Computer programming_sentence_75

Methods of measuring programming language popularity include: counting the number of job advertisements that mention the language, 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). Computer programming_sentence_76

Some languages are very popular for particular kinds of applications, while some languages are regularly used to write many different kinds of applications. Computer programming_sentence_77

For example, COBOL is still strong in corporate data centers often on large mainframe computers, Fortran in engineering applications, scripting languages in Web development, and C in embedded software. Computer programming_sentence_78

Many applications use a mix of several languages in their construction and use. Computer programming_sentence_79

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). Computer programming_sentence_80

Debugging Computer programming_section_11

Main article: Debugging Computer programming_sentence_81

Debugging is a very important task in the software development process since having defects in a program can have significant consequences for its users. Computer programming_sentence_82

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. Computer programming_sentence_83

Use of a static code analysis tool can help detect some possible problems. Computer programming_sentence_84

Normally the first step in debugging is to attempt to reproduce the problem. Computer programming_sentence_85

This can be a non-trivial task, for example as with parallel processes or some unusual software bugs. Computer programming_sentence_86

Also, specific user environment and usage history can make it difficult to reproduce the problem. Computer programming_sentence_87

After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. Computer programming_sentence_88

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. Computer programming_sentence_89

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. Computer programming_sentence_90

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. Computer programming_sentence_91

Scripting and breakpointing is also part of this process. Computer programming_sentence_92

Debugging is often done with IDEs like Eclipse, Visual Studio, Xcode, Kdevelop, NetBeans and Code::Blocks. Computer programming_sentence_93

Standalone debuggers like GDB are also used, and these often provide less of a visual environment, usually using a command line. Computer programming_sentence_94

Some text editors such as Emacs allow GDB to be invoked through them, to provide a visual environment. Computer programming_sentence_95

Programming languages Computer programming_section_12

Main articles: Programming language and List of programming languages Computer programming_sentence_96

Different programming languages support different styles of programming (called programming paradigms). Computer programming_sentence_97

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. Computer programming_sentence_98

Ideally, the programming language best suited for the task at hand will be selected. Computer programming_sentence_99

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. Computer programming_sentence_100

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. Computer programming_sentence_101

It is usually easier to code in "high-level" languages than in "low-level" ones. Computer programming_sentence_102

Allen Downey, in his book How To Think Like A Computer Scientist, writes: Computer programming_sentence_103

Computer programming_description_list_2

  • The details look different in different languages, but a few basic instructions appear in just about every language:Computer programming_item_2_10
    • Input: Gather data from the keyboard, a file, or some other device.Computer programming_item_2_11
    • Output: Display data on the screen or send data to a file or other device.Computer programming_item_2_12
    • Arithmetic: Perform basic arithmetical operations like addition and multiplication.Computer programming_item_2_13
    • Conditional Execution: Check for certain conditions and execute the appropriate sequence of statements.Computer programming_item_2_14
    • Repetition: Perform some action repeatedly, usually with some variation.Computer programming_item_2_15

Many computer languages provide a mechanism to call functions provided by shared libraries. Computer programming_sentence_104

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. Computer programming_sentence_105

Programmers Computer programming_section_13

Main article: Programmer Computer programming_sentence_106

See also: Software developer and Software engineer Computer programming_sentence_107

Computer programmers are those who write computer software. Computer programming_sentence_108

Their jobs usually involve: Computer programming_sentence_109

See also Computer programming_section_14

Main article: Outline of computer programming Computer programming_sentence_110

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: programming.