An array is a table of related variables, called elements, of uniform size stored in computer memory.

An array is given a single name and each element’s value is accessed using this arrayname and a subscript.

A subscript is a positive integer value that refers to an element’s position in the array. The subscript is written enclosed in parentheses following the arrayname. Subscripts may be represented in one of three ways:

 

Here is an example of a 12-element array named month:

month

Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
1	2	3	4	5	6	7	8	9	10	11	12

In this example:

• The arrayname is month
• The value of each element is a 3-character string
• The value of month( 1 ) is “Jan”
• The value of month( 2 ) is “Feb”
• If the integer variable  I  has a value of 3, then to refer to month( I ) is to refer to the value “Mar”
• If I = 5, then month( I + 1 ) refers to the value “Jun”

In many programming applications that involve large amounts of related data, the computer must be able to store all the related values at one time, rather than one at a time (as is the case with single variable input). For example, suppose we needed to have all the daily high temperatures for a year so we could compute the average temperature. But then also suppose we needed to know how much each day’s temperature deviated from that average.

To do this we need an array of 365 elements in which to place each day’s high temperature. Then we could, through the use of loop processing and a variable subscript, average all 365 values and then go back to the beginning of the array and, one at a time, compare each day’s temperature with that average – a task which would not be very practical without the use of an array.