Array (data structure): Difference between revisions

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.

The first digital computers used machine-language programming to set up and access array structures for data tables, vector and matrix computations, and for many other purposes. [[John von Neumann]] wrote the first array-sorting program ([[merge sort]]) in 1945, during the building of the [[EDVAC|first stored-program computer]].<ref>{{TAOCP|volume=3|page=159}}</ref> Array indexing was originally done by [[self-modifying code]], and later using [[index register]]s and [[Addressing mode|indirect addressing]]. Some mainframes designed in the 1960s, such as the [[Burroughs large systems|Burroughs B5000]] and its successors, used [[memory segmentation]] to perform index-bounds checking in hardware.<ref>{{citation|title=Capability-based Computer Systems|first=Henry M.|last=Levy|publisher=Digital Press|year=1984|isbn=9780932376220|page=22}}.</ref>

Arrays are used to implement other data structures, such as lists, [[heap (data structure)|heaps]], [[hash table]]s, [[double-ended queue|deque]]s, [[queue (data structure)|queue]]s, [[stack (data structure)|stacks]], [[String (computer science)|strings]], and VLists. Array-based implementations of other data structures are frequently simple and space-efficient ([[implicit data structure]]s), requiring little space [[Overhead (computing)|overhead]], but may have poor space complexity, particularly when modified, compared to tree-based data structures (compare a [[sorted array]] to a [[search tree]]).

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. They are known in this context 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.

As an example consider the C declaration <code>int anArrayName[10];</code> which declares a one-dimensional array of ten integers. Here, the array can store ten elements of type <code>int</code> . This array has indices starting from zero through nine. For example, the expressions <code>anArrayName[0]</code> and <code>anArrayName[9]</code> are the first and last elements respectively.