Creating arrays

An array is a data type which stores a collection of items.

It’s essentially a list of items, where:

• each item is the same data type (e.g. all integers, or all strings)
• the size of the array is fixed (i.e. it cannot grow or shrink)
• each item can be accessed by its index (i.e. its position in the list)

Declaring an array

We can declare an array using the type, followed by square brackets [], and the name of the array:

int[] numbers;

This declares an array of int values called numbers.

Note: we don’t declare the size of the array yet - that’s done when we initialise it.

Initialising an array

We can initialise an array using the new keyword, followed by the type, square brackets [], and the size of the array in the brackets:

int[] numbers;
numbers = new int[5];

This initialises the numbers array to hold 5 int values.

We can also declare and initialise an array in one line:

int[] numbers = new int[5];

Assigning values to an array

If we want to create an array called primes to hold the first 4 prime numbers, we can do this:

int[] primes = new int[4] { 2, 3, 5, 7 };

Note the use of curly braces {} to hold the values of the array. Any values in the array go inside them.

Creating arrays: examples

int[] nums;
nums = new int[3];
nums = [ 2, 4, 6 ]

bool[] studentsPassed = new bool[]{ true, false, false, true, true };