Lesson 21Collections

Arrays

Ordered Collections

Arrays store multiple values of the same type in an ordered list. They're one of the most commonly used data structures in programming!

Creating Arrays

With Values

[1, 2, 3]

Empty Array

[Int]()

Type Annotation

var arr: [String] = []

Repeated Values

Array(repeating: 0, count: 5)

Array Indexing

Index 0

Apple

Index 1

Banana

Index 2

Orange

Arrays start at index 0, not 1!

Common Operations

.append()

Add to end

.insert(at:)

Add at index

.remove(at:)

Remove by index

.count

Number of items

.contains()

Check if exists

.first/.last

Safe access

var vs let

var - Mutable array (can add/remove/change)
let - Immutable array (fixed contents)

main.swift

// Creating arrays
var fruits = ["Apple", "Banana", "Orange"]
let numbers: [Int] = [1, 2, 3, 4, 5]

// Empty arrays
var emptyArray: [String] = []
var anotherEmpty = [Int]()

// Array with repeated values
var zeros = Array(repeating: 0, count: 5)
print(zeros) // [0, 0, 0, 0, 0]

// Accessing elements by index (0-based)
print(fruits[0])  // Apple (first)
print(fruits[1])  // Banana (second)
print(fruits[2])  // Orange (third)

// Safe access with first and last
print(fruits.first ?? "Empty")  // Apple
print(fruits.last ?? "Empty")   // Orange

// Array properties
print("Count: \(fruits.count)")      // 3
print("Is empty: \(fruits.isEmpty)") // false

// Adding elements
fruits.append("Mango")             // Add to end
fruits.insert("Grape", at: 0)      // Add at index
fruits += ["Kiwi", "Peach"]        // Add multiple
print(fruits)

// Modifying elements
fruits[0] = "Green Grape"
print(fruits[0]) // Green Grape

// Removing elements
let removed = fruits.remove(at: 0)  // Remove by index
print("Removed: \(removed)")

fruits.removeLast()   // Remove last
fruits.removeFirst()  // Remove first
// fruits.removeAll()  // Remove all

// Checking contents
print(fruits.contains("Apple"))  // Check if exists

// Finding index
if let index = fruits.firstIndex(of: "Mango") {
    print("Mango is at index \(index)")
}

Try It Yourself!

Create an array of your favorite movies, add a new one, remove one you don't like, and print how many movies are in your list!