Array (data structure): Difference between revisions

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{{More citations needed|date=September 2008}}

In [[computer science]], an '''array''' is a [[data structure]] consisting of a collection of ''elements'' ([[value (computer science)|values]] or [[variable (programming)|variables]]), of same memory size, each identified by at least one ''array index'' or ''key'', a collection of which may be a [[tuple]], known as an index tuple. An array is stored such that the position (memory address) of each element can be computed from its index [[tuple]] by a mathematical formula.<ref>{{cite web|url=https://xlinux.nist.gov/dads/HTML/array.html|title=array|last=Black|first=Paul E.|date=13 November 2008|work=[[Dictionary of Algorithms and Data Structures]]|publisher=[[National Institute of Standards and Technology]]|access-date=22 August 2010}}</ref><ref name="andres">{{cite arXiv |eprint=1008.2909 |author1=Bjoern Andres |author2=Ullrich Koethe |author3=Thorben Kroeger |author4=Hamprecht |title=Runtime-Flexible Multi-dimensional Arrays and Views for C++98 and C++0x |class=cs.DS |year=2010}}</ref><ref name="garcia">{{Cite journal|last1=Garcia|first1=Ronald |first2=Andrew |last2=Lumsdaine|year=2005|title=MultiArray: a C++ library for generic programming with arrays|journal=Software: Practice and Experience|volume=35|issue=2|pages=159–188|issn=0038-0644|doi=10.1002/spe.630|s2cid=10890293 }}</ref> The simplest type of data structure is a linear array, also called a one-dimensional array.

For example, an array of ten [[32-bit]] (4-byte) integer variables, with indices 0 through 9, may be stored as ten [[Word (data type)|words]] at memory addresses 2000, 2004, 2008, ..., 2036, (in [[hexadecimal]]: <code>0x7D0</code>, <code>0x7D4</code>, <code>0x7D8</code>, ..., <code>0x7F4</code>) so that the element with index ''i'' has the address 2000 + (''i'' × 4).<ref>David R. Richardson (2002), The Book on Data Structures. iUniverse, 1121112 pages. {{ISBN|0-595-24039-9}}, {{ISBN|978-0-595-24039-5}}.</ref>

The memory address of the first element of an array is called first address, foundation address, or base address.

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One or more large arrays are sometimes used to emulate in-program [[dynamic memory allocation]], particularly [[memory pool]] allocation. Historically, this has sometimes been the only way to allocate "dynamic memory" portably.

Arrays can be used to determine partial or complete [[control flow]] in programs, as a compact alternative to (otherwise repetitive) multiple <code>IF</code> statements. TheyIn arethis knowncontext, inthey thisare contextknown as [[control table]]s and are used in conjunction with a purpose-built interpreter whose [[control flow]] is altered according to values contained in the array. The array may contain [[subroutine]] [[Pointer (computer programming)|pointers]] (or relative subroutine numbers that can be acted upon by [[Switch statement|SWITCH]] statements) that direct the path of the execution of the program.

==Element identifier and addressing formulas==