Swift Arrays

An array stores multiple values of the same type in an ordered list. Each value sits at a numbered position called an index. Arrays are one of the most used data structures in Swift programming.

The Train Compartment Analogy

┌─────────────────────────────────────────────────┐
│  Array = A train with numbered compartments     │
│                                                 │
│  Index:  [0]      [1]      [2]      [3]         │
│  Value:  "Apple"  "Mango"  "Banana" "Grapes"    │
│                                                 │
│  Each compartment holds one item.               │
│  The first compartment is always index 0.       │
└─────────────────────────────────────────────────┘

Creating an Array

// With values
let fruits = ["Apple", "Mango", "Banana"]

// Empty array with type annotation
var scores: [Int] = []

// Another empty array syntax
var names = [String]()

Accessing Elements

let cities = ["Delhi", "Mumbai", "Chennai", "Kolkata"]

print(cities[0])   // Delhi
print(cities[2])   // Chennai
print(cities.first ?? "None")   // Delhi
print(cities.last ?? "None")    // Kolkata

Array indexes start at 0. Accessing an index that does not exist crashes your app, so always verify the index or use safe access like first and last.

Array Properties

let numbers = [10, 20, 30, 40, 50]

print(numbers.count)       // 5
print(numbers.isEmpty)     // false
print(numbers.contains(30)) // true

Adding Elements

var colors = ["Red", "Green"]

colors.append("Blue")           // adds at end
colors.insert("Yellow", at: 1) // adds at index 1

print(colors)   // ["Red", "Yellow", "Green", "Blue"]

Removing Elements

var animals = ["Cat", "Dog", "Fish", "Bird"]

animals.remove(at: 1)      // removes "Dog"
animals.removeLast()       // removes "Bird"
animals.removeFirst()      // removes "Cat"

print(animals)   // ["Fish"]

Updating Elements

var temps = [30, 32, 28, 35]
temps[2] = 31
print(temps)   // [30, 32, 31, 35]

Iterating Over an Array

let languages = ["Swift", "Python", "Java"]

// With value only
for lang in languages {
    print(lang)
}

// With index and value
for (index, lang) in languages.enumerated() {
    print("\(index): \(lang)")
}
// 0: Swift
// 1: Python
// 2: Java

Array Operations

let a = [1, 2, 3]
let b = [4, 5, 6]
let combined = a + b
print(combined)   // [1, 2, 3, 4, 5, 6]

Useful Array Methods

var nums = [5, 2, 8, 1, 9, 3]

print(nums.sorted())             // [1, 2, 3, 5, 8, 9]
print(nums.reversed())           // [3, 9, 1, 8, 2, 5]
print(nums.min()!)               // 1
print(nums.max()!)               // 9

let doubled = nums.map { $0 * 2 }
print(doubled)   // [10, 4, 16, 2, 18, 6]

let evens = nums.filter { $0 % 2 == 0 }
print(evens)     // [2, 8]

2D Arrays – Array of Arrays

let grid = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

print(grid[1][2])   // 6  (row 1, column 2)

┌─────────────────────────────────┐
│  grid visualised as a matrix    │
│                                 │
│  [0] → 1  2  3                  │
│  [1] → 4  5  6                  │
│  [2] → 7  8  9                  │
│                                 │
│  grid[1][2] = row 1, col 2 = 6  │
└─────────────────────────────────┘