Data structures are formats for storing data - like arrays, records, and files.

An array is a data structure that can store a group of data of the same type under a single identifier.

Each piece of data within an array is called an element. Each element can be accessed by its index (position) in the array.

Example 1 shows how to create and manipulate arrays in pseudo-code.

Example 1
Use square brackets to define an array
names ← ["Adam", "Bob", "Charlie", "Daniel"]

Elements in arrays can be retrieved just like characters in strings
OUTPUT names[2]
>>> "Charlie"

Remember: indexing starts at 0

Elements can be changed as well
names[1] = "Ben"
OUTPUT names
>>> ["Adam", "Ben", "Charlie", "Daniel"]

Just like with strings, LEN returns the length of an array
OUTPUT LEN(names)
>>> 4

Two-dimensional (2D) arrays are arrays of arrays.

Example 2 shows the manipulation of a 2D array.

Example 2
Five students' Maths and English scores are shown in this 2D array
Each array inside this 2D array contains a certain student's two test scores
scores ← [[9, 15], [18, 8], [12, 14], [13, 7], [10, 17]]

Retrieve the fourth student's scores
OUTPUT scores[3]
>>> [13, 7]

Retrieve the second student's first score
OUTPUT scores[1][0]
>>> 18

Get the length of the 2D array
OUTPUT LEN(scores)
>>> 5

Get the length of the first element
OUTPUT LEN(scores[0])
>>> 2


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Can you think of other uses for 2D arrays?

Storing the pixel data of images, board games where the board is a grid, and much more.

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