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In [[computer science]], '''source code''' is any collection of statements or declarations written in some [[human-readable]] computer [[programming language]].  Source code is the means most often used by [[programmer]]s to specify the actions to be performed by a computer.

The source code which constitutes a [[computer program|program]] is usually held in one or more [[text file]]s, sometimes stored in databases as [[stored procedure]]s and may also appear as [[code snippets]] printed in books or other media.  A large collection of source code files may be organized into a [[Directory (file systems)|directory tree]], in which case it may also be known as a '''source tree'''.
 
A computer program's source code is the collection of files needed to convert from human-readable form to some kind of computer-executable form.  The source code may be converted into an [[executable]] file by a [[compiler]], or executed [[on the fly]] from the human readable form with the aid of an [[interpreter (computing)|interpreter]].

The '''code base''' of a [[programming]] project is the larger collection of all the source code of all the [[computer program]]s which make up the project.

== Organization ==
The source code for a particular piece of software may be contained in a single file or many files. Though the practice is uncommon, a program's source code can be written in different programming languages.<ref>Extending and Embedding the Python Interpreter — Python v2.6 Documentation [http://docs.python.org/extending/]</ref> For example, a program written primarily in the [[C (programming language)|C programming language]], might have portions written in [[Assembly language]] for optimization purposes. It is also possible for some components of a piece of software to be written and compiled separately, in an arbitrary programming language, and later integrated into the software using a technique called [[library linking]]. This is the case in some languages, such as [[Java (programming language)|Java]]: each class is compiled separately into a file and linked by the interpreter at runtime. 

Yet another method is to make the main program an interpreter for a programming language{{Fact|date=May 2008}}, either designed specifically for the application in question or general-purpose, and then write the bulk of the actual user functionality as [[Macro (computer science)|macros]] or other forms of add-ins in this language, an approach taken for example by the [[GNU Emacs]] text editor.

Moderately complex software customarily requires the compilation or assembly of several, sometimes dozens or even hundreds, of different source code files. In these cases, instructions for compilations, such as a [[Makefile]], are included with the source code. These describe the relationships among the source code files, and contain information about how they are to be compiled. 

The [[revision control]] system is another tool frequently used by developers for source code maintenance.

== Purposes ==
Source code is primarily used as input to the process that produces an executable program (ie., it is [[compiler|compiled]] or [[Interpreter (computing)|interpreted]]). It is also used as a method of communicating [[algorithm]]s between people (eg., [[code snippets]] in books).<ref name="Spinellis">Spinellis, D: ''Code Reading: The Open Source Perspective''. Addison-Wesley Professional, 2003. ISBN 0-201-79940-5</ref>

[[Programmers]] often find it helpful to review existing source code to learn about programming techniques.<ref name="Spinellis" /> The sharing of source code between developers is frequently cited as a contributing factor to the maturation of their programming skills.<ref name="Spinellis" /> Some people consider source code an expressive [[Media (arts)|artistic medium]].<ref>"''Art and Computer Programming''" [http://www.onlamp.com/pub/a/onlamp/2005/06/30/artofprog.html ONLamp.com], (2005)</ref>

[[Porting]] software to other [[computer platform]]s is usually prohibitively difficult without source code. Without the source code for a particular piece of software, portability is generally computationally expensive {{Fact|date=October 2008}}.  Possible porting options include [[binary translation]] and emulation of the original platform.

[[Decompilation]] of an executable program can be used to generate source code, either in [[assembly code]] or in a [[high level language]].

Programmers frequently adapt source code from one piece of software to use in other projects, a concept known as [[software reusability]].

== Licensing ==
{{main|software license}}
Software, and its accompanying source code, typically falls within one of two licensing paradigms: [[free software]] and [[proprietary software]]. <br /><br />
Generally speaking, software is ''free'' if the source code is free to use, distribute, modify and study, and ''proprietary'' if the source code is kept secret, or is privately owned and restricted. Note that "free" refers to freedom, not price. Under many licenses it is acceptable to charge for "free software". The first free software license to be published and to explicitly grant these freedoms was the [[GNU General Public License]] in 1989. The GNU GPL was originally intended to be used with the [[GNU operating system]]. The GNU GPL was later adopted by other non-GNU software projects such as the [[Linux kernel]].<br /><br />
For proprietary software, the provisions of the various copyright laws, [[trade secret|trade secrecy]] and [[patent]]s are used to keep the source code closed.  Additionally, many pieces of [[retail software]] come with an [[Software license agreement|end-user license agreement]] (EULA) which typically prohibits [[decompilation]], [[reverse engineering]], analysis, modification, or circumventing of [[copy protection]].  Types of source code protection -- beyond traditional [[compiler|compilation]] to [[object code]] -- include code encryption, [[code obfuscation]] or [[code morphing]].

== Legal issues in the United States ==
{{update}}
In a 2003 court case in the United States, the court{{which|date=June 2010|there are quite a few courts in the U.S.; Supreme Court?}} ruled that source code should be considered a Constitutionally protected form of [[free speech]]. Proponents of free speech argued that because source code conveys information to programmers, is written in a language, and can be used to share humour and other artistic pursuits, it is a protected form of communication.

One of the first court cases regarding the nature of source code as free speech involved [[University of California]] [[mathematics]] professor [[Dan Bernstein]], who had published on the internet the source code for an [[encryption]] program that he created. At the time, encryption algorithms were classified as [[munition]]s by the United States government; exporting encryption to other countries was considered an issue of [[national security]], and had to be approved by the [[United States Department of State|State Department]]. The [[Electronic Frontier Foundation]] sued the [[Federal government of the United States|U.S. government]] on Bernstein's behalf; the court ruled that source code was free speech, protected by the First Amendment.

== Quality ==
{{main|Software quality}}
The way a program is written can have important consequences for its maintainers. Many source code [[programming style]] guides, which stress readability and some language-specific conventions are aimed at the maintenance of the software source code, which involves debugging and updating. Other priorities, such as the speed of the programs execution, or the ability to compile the program for multiple architectures, often make code readability a less important consideration, since code ''quality'' depends entirely on its ''purpose''.

== See also ==
{{Wiktionarypar|source code}}
* [[China Compulsory Certificate]]
* [[Legacy code]]
* [[Machine code]]
* [[Open-source software]]
* [[Obfuscated code]]
* [[Object code]]
* [[Programming language]]
* [[Programming style]]
* [[Source code repository]]
* [[Syntax highlighting]]

== References ==
<references />
* (VEW04) "Using a Decompiler for Real-World Source Recovery", M. Van Emmerik and T. Waddington, the ''Working Conference on Reverse Engineering'', [[Delft]], [[Netherlands]], 9-12 November 2004. [http://www.itee.uq.edu.au/~emmerik/experience_long.pdf Extended version of the paper].

== External links ==
* [http://www.linfo.org/source_code.html Source Code Definition] - by The [[Linux]] Information Project (LINFO)
* [http://www.google.com/codesearch? Google public source code search]
* [http://codewiki.wikispaces.com/ A publicly editable wiki of source code]
* [http://www.sourcepod.com/ Online source code sharing]
* {{cite web| title=Obligatory accreditation system for IT security products (2008-09-22), may start from May 2009, reported by Yomiuri on 2009-04-24.|url=http://www.metafilter.com/75061/Obligatory-accreditation-system-for-IT-security-products|publisher=MetaFilter.com|accessdate=2009-04-24}}
* [http://www.programmer2programmer.net/project.aspx Programmer2programmer.Net - Live project source code]
* [http://www.SourceCodeHub.com SourceCodeHub.com] - project source codes
*[https://c.happy codings.com/functions/ C Programming Example Codes]

[[Category:Source code|*]]

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