Arrays (OCR GCSE Computer Science): Revision Notes

Arrays

An array is a data structure used to store multiple values of the same data type in a single variable. Arrays are particularly useful when solving problems that require the storage of large amounts of related data, such as lists of names or scores.

Key Characteristics of Arrays

• Arrays have a fixed length or static structure, meaning the size of the array is defined when it is created and cannot be changed.
• Arrays can be one-dimensional (1D) or two-dimensional (2D). A 1D array is like a list, while a 2D array is like a grid or table with rows and columns.
• 2D arrays can be used to emulate database tables, where each row is a record and each column is a field. This is useful for storing structured data like spreadsheets.

One-Dimensional Arrays (1D)

A 1D array stores a simple list of values, accessed using an index starting from 0.

Operation	Example
Creating a 1D Array	names = ["Bob", "Alex", "Chris"]
Accessing an Item	names[1] → Output: Alex (index starts at 0)
Looping through a 1D Array	for name in names: print(name)
Length of a 1D Array	len(names) → Output: 3
Summing Items in an Array	scores = [5, 12, 5, 7, 8] total = sum(scores) → Output: 37

Two-Dimensional Arrays (2D)

A 2D array stores data in a grid, allowing access using two indices: one for the row and one for the column. It's useful for working with more complex data like tables.

Operation	Example
Creating a 2D Array	matrix = [[1, 2], [3, 4], [5, 6]] (3 rows and 2 columns)
Accessing an Item	matrix[1][1] → Output: 4 (Row 1, Column 1)
Looping through a 2D Array	for row in matrix: for col in row: print(col)
Emulating a Table	customers = [["John", "London"], ["Jane", "Paris"]]
Length of a 2D Array	len(matrix) → Output: 3 (number of rows)