Arrays

An array is a data structure   which groups related items together

• related in that they record similar data about several different things
  • the mark on a test for each student in a class
  • the temperature on the hour, at each hour during a day
  • etc

Array index vs. array element

Think of an array as a collection of letter boxes:

• each has a label on it, so each can be identified individually
  • numbered from "low" to "high", or 1..8, in the picture below
• each can store an item of information (the same type of thing in each one)

When designing an array, you need to decide

• what the labels are going to be
  • the array index
  • what type  of value is the index?
  • what range  of values can the index take?
  • the array index may be INTEGER, CHARACTER or any ENUMERATED TYPE
• what type of information can go into each box.
  • the array element  type
  • the array element type can be any  type
• the type of the array index is not related to the type of the array items

Examples

The picture below shows three example array types. They are similar to the extent that each can store 8 items of data, but they differ in what can be stored and how each element is labelled:

• INTEGER(1..8)
  • element type is INTEGER
  • index type is INTEGER
  • index can take 8 possible values, ranging from 1..8
• FLOAT('a'..'h')
  • element type is FLOAT
  • index type is CHARACTER
  • index can take 8 possible values, ranging from 'a'..'h'
• STRING(-5..2)
  • element type is STRING
  • index type is INTEGER
  • index can take 8 possible values, ranging from -5..2