## Arrays WHAT IS AN ARRAY? An array is a type of data structure used to store information. Data structures are used to organize, arrange, and access collections of information.

Arrays are the most basic data structures. Take a moment to look at the diagram above. Take note of the following:

• The array has a length of 10

• The index positions start at 0 and end with 9

• Thus the final index is equal to length - 1

CREATING AN ARRAY

When you want to create an array, you'll need to do three things:

Declaration

• Works like any other variable

• Usually at the top of your program

Initialize The Array

• Need to manually allocate memory

• If you skip this step, you'll get a NullPointerException

• Usually done in setup()

Initialize Each Element

• Gives the actual data starting values

• You can skip this step if you're okay with everything starting at zero

Example

int[] numbers;

void setup()
{

numbers = new int;

for(int i = 0; i < numbers.length; i++)

{

numbers[i] = (int) (Math.random() * 10);

}

} USING ARRAYS

## Accessing an element

• To access an element, you will reference it by its index position:

System.out.println(numbers);

## Set an element

• To set an element, you do the same thing but on the left hand side:

numbers = 74;

## Get the length

• To get the number of elements in an array, you use the length property.

if(numbers.length < 5) TWO DIMENSIONAL ARRAYS

Two dimensional arrays are not officially part of the course this year, but I've provided a quick summary here for students who want to explore them!

## Rows and Columns

• A row is a horizontal line of data. Think the motion of rowing a boat.

• A column is a vertical line of data. Think about the structure of a column holding up a building.

• Rows are listed before columns when accessing an index position.

## Syntax

• When using a two dimensional array, we simply double everything!

• Most commonly, we'll make variables or constants to keep track of rows and columns to help our code be more readable. Examples

final int ROWS = 100;

final int COLS = 50;

char [] grid = new char[ROWS][COLS]

for(int i = 0; i < COLS; i++)

{

for(int j = 0; j < ROWS; j++)

{

grid[i][j] = "-";

}

}

println(grid);

RESOURCES Chapter 9 - Arrays (p163)

Overview of Arrays in One Video

9.1 - What is An Array (Concepts)

9.2 - Coding an Array

9.3 - Using Objects with an Array
(This includes new stuff we haven't learned)

9.4 - Using Loops an Array of Objects
(This includes new stuff we haven't learned)