Arrays in Pseudocode (1D and 2D)

If you needed to store the names of three students, you could easily create three separate variables: student1, student2, and student3. But what if you needed to store the names of 10,000 students? Declaring 10,000 individual variables is impossible.

This is the exact problem that Arrays solve. An array is a single data structure that can hold multiple items of the same data type under one single identifier. You access these items using an "index" (a number representing their position).

In this guide, we will explore the core concepts of both one-dimensional (1D) and two-dimensional (2D) arrays, and outline the strict declaration rules required by major exam boards like AQA, OCR, and Cambridge (CIE).

Core Concepts: Understanding Arrays

Arrays are contiguous blocks of memory. This means the items are stored right next to each other. Because of this, arrays traditionally have a fixed, static size that cannot change once created.

1D Arrays and Indexing

A one-dimensional array is like a list. To access or change a specific value, you use square brackets [] containing the index number. Note: Most programming languages (and the AQA/OCR specs) use 0-based indexing, meaning the first item is at index 0, not 1.

Iterating Through Arrays

The true power of an array is unlocked when combined with a FOR loop. Because indices are sequential numbers, you can use the loop's counter variable to automatically step through every single item in the array.

2D Arrays (Matrices)

A two-dimensional array is simply an array of arrays. You can visualize it as a grid or a table with rows and columns (like a chessboard or a spreadsheet). To access an item, you need two indices: [row, column].

Syntax Variations by Exam Board

While indexing logic is universal, how you explicitly declare the array and its size varies massively depending on your specification.

AQA Pseudocode Standard

AQA assumes 0-based indexing unless stated otherwise in the question. AQA does not require explicit dimension declarations; you simply assign a list of items using the left arrow <-.

OCR Pseudocode Standard

OCR syntax is explicitly 0-based. When declaring an array, you must use the array keyword followed by the identifier and its size in brackets.

Cambridge (CIE / 9618) Standard

The CIE standard is the strictest. You must explicitly declare the upper and lower bounds of the array, as well as the data type it holds. CIE arrays traditionally start at index 1.

Conclusion

Arrays are the foundation of data processing. Without them, algorithms like Bubble Sort or Binary Search wouldn't be possible, as there would be no clean way to loop through a sequence of data.

When taking your exams, pay very close attention to whether the array uses 0-based or 1-based indexing, as this will dictate how you write your FOR loops (e.g., looping from 0 to length-1 versus 1 to length). Always conform to your board's explicit declaration rules to secure full marks.