Cambridge Syllabus Notes

Arrays 📚

What is an Array?

An array is a collection of multiple values of the same data type stored in a single variable. Think of it as a row of lockers where each locker holds one item of the same type.

Declaring an Array

int[] scores = new int[5];

Here, int[] tells the computer that scores will hold integers, and new int[5] creates space for 5 of them.

Indexing: Accessing Elements

Array indices start at 0. The first element is scores[0], the second scores[1], and so on.

Assign a value: scores[0] = 88;
Retrieve a value: int first = scores[0];

Array Size and Length

The size is fixed once created. Use scores.length to get the number of elements.

int size = scores.length;  // size = 5

Common Operations

Loop through an array: for (int i = 0; i < scores.length; i++) { … }
Find the maximum: iterate and compare.
Calculate the average: sum all elements and divide by scores.length.

Example: Storing Test Scores

Index	Score
0	88
1	92
2	76
3	85
4	90

To calculate the average:

int sum = 0;
for (int i = 0; i < scores.length; i++) {
    sum += scores[i];
}
double avg = (double)sum / scores.length;  // avg = 86.6

Analogy: The Array as a Playlist

Imagine an array as a music playlist. Each song (element) is stored in a specific order. You can jump to song number 3 (index 2) and play it instantly.

Exam Tips 📌

Remember that array indices start at 0, not 1.
Use array.length to avoid IndexOutOfBoundsException.
When asked to calculate the sum or average, show the loop and the final formula.
For array sorting questions, mention that you can use Arrays.sort(array) or write a simple bubble sort loop.
Practice writing code that initialises an array with values directly: int[] nums = {1, 2, 3, 4};

Quick Quiz

What will int[] a = new int[3]; a[0] = 5; print if you output a[0]?
Write a loop that prints all elements of int[] b = {10, 20, 30};.
How many elements can you access in int[] c = new int[10];?

Use arrays to store multiple values of the same data type