In computer science
, an array data structure
, or simply an array
, is a data structure
consisting of a collection of elements
), each identified by at least one array index
. An array is stored so that the position of each element can be computed from its index tuple
by a mathematical formula.
The simplest type of data structure is a linear array, also called one-dimensional array.
For example, an array of 10 32-bit integer variables, with indices 0 through 9, may be stored as 10 words
at memory addresses 2000, 2004, 2008, ... 2036, so that the element with index i
has the address 2000 + 4 × i
The memory address of the first element of an array is called first address or foundation address.
Because the mathematical concept of a matrix
can be represented as a two-dimensional grid, two-dimensional arrays are also sometimes called matrices. In some cases the term "vector" is used in computing to refer to an array, although tuples
rather than vectors
are more correctly the mathematical equivalent. Arrays are often used to implement tables
, especially lookup tables
; the word table
is sometimes used as a synonym of array
Arrays are among the oldest and most important data structures, and are used by almost every program. They are also used to implement many other data structures, such as lists
. They effectively exploit the addressing logic of computers. In most modern computers and many external storage
devices, the memory is a one-dimensional array of words, whose indices are their addresses. Processors
, especially vector processors
, are often optimized for array operations.
Arrays are useful mostly because the element indices can be computed at run time
. Among other things, this feature allows a single iterative statement
to process arbitrarily many elements of an array. For that reason, the elements of an array data structure are required to have the same size and should use the same data representation. The set of valid index tuples and the addresses of the elements (and hence the element addressing formula) are usually,
but not always,
fixed while the array is in use.
The term array
is often used to mean array data type
, a kind of data type
provided by most high-level programming languages
that consists of a collection of values or variables that can be selected by one or more indices computed at run-time. Array types are often implemented by array structures; however, in some languages they may be implemented by hash tables
, linked lists
, search trees
, or other data structures.
The term is also used, especially in the description of algorithms
, to mean associative array
or "abstract array", a theoretical computer science
model (an abstract data type
or ADT) intended to capture the essential properties of arrays. Arrays have better cache locality as compared to linked lists