What is an array?
An array is a data structure that stores many values of the same type under one name. Instead of using ten separate variables for ten marks, you use one array of ten elements. Each element is reached by its index (its position number).
Key idea
In most programming languages a one-dimensional array is indexed from 0. So an array of size 5 has valid indexes 0, 1, 2, 3, 4 - the last index is size − 1.
Using elements
You read or change one element by writing its index in brackets. If mark is an array, mark[0] is the first element and mark[4] is the fifth. Notice that the index is always one less than the counting position, because indexing starts at 0. Writing to an element, such as mark[2] = 80, changes just that one value and leaves the rest untouched.
Example
Given score = [90, 75, 60, 88]: score[0] is 90, score[2] is 60, and the array has 4 elements so the highest valid index is 3. Using score[4] would be an error (index out of range).
Why arrays help
Because elements share one name and are numbered, a loop can visit every element easily - for example adding all the marks by stepping the index from 0 to size − 1. This makes arrays ideal for lists of data such as marks, names or temperatures.
Remember
- All elements of an array have the same data type.
- Indexing usually starts at 0; the last index = size − 1.
- An index outside the range causes an out-of-range error.