Computer programming

Computer programming (often shortened to programming or coding) is the process of

writing, testing, debugging/troubleshooting, and maintaining the source code of

computer programs. This source code is written in a programming language. The code

may be a modification of an existing source or something completely new. The purpose

of programming is to create a program that exhibits a certain desired behavior

(customization). The process of writing source code often requires expertise in many

different subjects, including knowledge of the application domain, specialized

algorithms and formal logic.
Overview

Within software engineering, programming (the implementation) is regarded as one

phase in a software development process.

There is an ongoing debate on the extent to which the writing of programs is an art, a

craft or an engineering discipline.[1] Good programming is generally considered to be

the measured application of all three, with the goal of producing an efficient and

evolvable software solution (the criteria for "efficient" and "evolvable" vary

considerably). The discipline differs from many other technical professions in that

programmers generally do not need to be licensed or pass any standardized (or

governmentally regulated) certification tests in order to call themselves "programmers"

or even "software engineers." However, representing oneself as a "Professional

Software Engineer" without a license from an accredited institution is illegal in many

parts of the world.

Another ongoing debate is the extent to which the programming language used in

writing computer programs affects the form that the final program takes. This debate is

analogous to that surrounding the Sapir-Whorf hypothesis [2] in linguistics, that

postulates that a particular language's nature influences the habitual thought of its

speakers. Different language patterns yield different patterns of thought. This idea

challenges the possibility of representing the world perfectly with language, because it

acknowledges that the mechanisms of any language condition the thoughts of its

speaker community.

Said another way, programming is the craft of transforming requirements into

something that a computer can execute.

History of programming

See also: History of programming languages

Wired plug board for an IBM 402 Accounting Machine.

The concept of devices that operate following a pre-defined set of instructions traces

back to Greek Mythology, notably Hephaestus and his mechanical servants[3]. The

Antikythera mechanism was a calculater utilizing gears of various sizes and

configuration to determine its operation. The earliest known programmable machines

(machines whose behavior can be controlled and predicted with a set of instructions)

were Al-Jazari's programmable Automata in 1206.[4] One of Al-Jazari's robots was

originally a boat with four automatic musicians that floated on a lake to entertain

guests at royal drinking parties. Programming this mechanism's behavior meant placing

pegs and cams into a wooden drum at specific locations. These would then bump into

little levers that operate a percussion instrument. The output of this device was a

small drummer playing various rhythms and drum patterns.[5][6] Another sophisticated

programmable machine by Al-Jazari was the castle clock, notable for its concept of

variables which the operator could manipulate as necessary (i.e. the length of day and

night). The Jacquard Loom, which Joseph Marie Jacquard developed in 1801, uses a

series of pasteboard cards with holes punched in them. The hole pattern represented

the pattern that the loom had to follow in weaving cloth. The loom could produce

entirely different weaves using different sets of cards. Charles Babbage adopted the

use of punched cards around 1830 to control his Analytical Engine. The synthesis of

numerical calculation, predetermined operation and output, along with a way to

organize and input instructions in a manner relatively easy for humans to conceive and

produce, led to the modern development of computer programming.

Development of computer programming accelerated through the Industrial Revolution.

The punch card innovation was later refined by Herman Hollerith who, in 1896 founded

the Tabulating Machine Company (which became IBM). He invented the Hollerith

punched card, the card reader, and the key punch machine. These inventions were the

foundation of the modern information processing industry. The addition of a plug-board

to his 1906 Type I Tabulator allowed it to do different jobs without having to be

physically rebuilt. By the late 1940s there were a variety of plug-board programmable

machines, called unit record equipment, to perform data processing tasks (card

reading). Early computer programmers used plug-boards for the variety of complex

calculations requested of the newly invented machines.
Data and instructions could be stored on external punch cards, which were kept in order

and arranged in program decks.

The invention of the Von Neumann architecture allowed computer programs to be

stored in computer memory. Early programs had to be painstakingly crafted using the

instructions of the particular machine, often in binary notation. Every model of

computer would be likely to need different instructions to do the same task. Later

assembly languages were developed that let the programmer specify each instruction in

a text format, entering abbreviations for each operation code instead of a number and

specifying addresses in symbolic form (e.g. ADD X, TOTAL). In 1954 Fortran, the first

higher level programming language, was invented. This allowed programmers to specify

calculations by entering a formula directly (e.g. Y = X*2 + 5*X + 9). The program text,

or source, was converted into machine instructions using a special program called a

compiler. Many other languages were developed, including ones for commercial

programming, such as COBOL. Programs were mostly still entered using punch 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 so programs could

be created by typing directly into the computers. Text editors were developed that

allowed changes and corrections to be made much more easily than with punch cards.

As time has progressed, computers have made giant leaps in the area of processing

power. This has brought about newer programming languages that are more abstracted

from the underlying hardware. Although these more abstracted languages require

additional overhead, in most cases the huge increase in speed of modern computers

has brought about little performance decrease compared to earlier counterparts. The

benefits of these more abstracted languages is that they allow both an easier learning

curve for people less familiar with the older lower-level programming languages, and

they also allow a more experienced programmer to develop simple applications quickly.

Despite these benefits, large complicated programs, and programs that are more

dependent on speed still require the faster and relatively lower-level languages with

today's hardware. (The same concerns were raised about the original Fortran language.)

Throughout the second half of the twentieth century, programming was an attractive

career in most developed countries. Some forms of programming have been increasingly

subject to offshore outsourcing (importing software and services from other countries,

usually at a lower wage), making programming career decisions in developed countries

more complicated, while increasing economic opportunities in less developed areas. It

is unclear how far this trend will continue and how deeply it will impact programmer

wages and opportunities.
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