Swift Arrays

So far in our Swift journey, we've worked with single values — a name here, a number there. But what happens when you need to store a whole squad of values? 🤔

That's where arrays come in.

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🧠 Why Do Arrays Exist?

Imagine you're building an app that tracks all the characters from Attack on Titan. You could do this:

let character1 = "Eren"
let character2 = "Mikasa"
let character3 = "Armin"
let character4 = "Levi"

Sure, that works for four characters. But what about all 100+ members of the Survey Corps? 😅 That approach falls apart fast.

This is exactly why Swift gives us arrays — a single place to store as many values as you need, always in the order you added them.

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📦 Creating Your First Array

Arrays use square brackets [], with commas between each item:

var surveyCorps = ["Eren", "Mikasa", "Armin", "Levi"]
let episodeCounts = [13, 12, 22, 16, 28]
var ratings = [9.8, 8.7, 9.5, 7.6]

Three things to notice here:

• Strings → wrapped in quotes ""
• Integers → plain numbers
• Doubles → numbers with a decimal point

Swift is smart enough to figure out the type of each array just by looking at what's inside. 🧐

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🔢 Reading Values — Zero Indexing

Here's the part that trips up almost every beginner (don't worry, it gets natural fast):

Arrays in Swift start counting from 0, not 1.

This is called zero-based indexing. So:

Position	Index	Value
1st	[0]	"Eren"
2nd	[1]	"Mikasa"
3rd	[2]	"Armin"
4th	[3]	"Levi"

print(surveyCorps[0]) // Eren
print(surveyCorps[1]) // Mikasa
print(surveyCorps[3]) // Levi

⚠️ Watch out! If you try to access an index that doesn't exist, Swift will crash your app on purpose. For example:

print(surveyCorps[99]) // 💥 CRASH

That might sound scary, but it's actually Swift protecting you. If it didn't crash, you'd silently get back garbage data — which is way worse than a crash you can see and fix. Think of it as Swift saying "Hey! That character doesn't exist in this arc!" 😤

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➕ Adding Items to an Array

If your array is a var (variable), you can keep adding to it using .append():

var surveyCorps = ["Eren", "Mikasa", "Armin"]

surveyCorps.append("Levi")
surveyCorps.append("Hange")
surveyCorps.append("Connie")

print(surveyCorps)
// ["Eren", "Mikasa", "Armin", "Levi", "Hange", "Connie"]

You can even append the same value more than once — Swift won't stop you:

surveyCorps.append("Eren") // Eren again? Okay then 😅

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🚫 Type Safety — One Type Per Array

Swift is very strict about this: an array can only hold one type of data.

var ratings = [9.8, 8.7, 9.5]
ratings.append("Mikasa") // ❌ ERROR — can't add a String to a Double array

This is type safety in action. Once Swift knows your array holds Double values, it won't let anything else sneak in. This keeps your data clean and your app stable. 🔒

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🏗️ Creating Empty Arrays

Sometimes you don't have data yet — you want to start empty and fill it in as you go. Here are two ways to do that:

Explicit syntax:

var titanShifters = Array<String>()
titanShifters.append("Attack Titan")
titanShifters.append("Armored Titan")
titanShifters.append("Colossal Titan")

Shorthand syntax (more common):

var titanShifters = [String]()
titanShifters.append("Attack Titan")
titanShifters.append("Armored Titan")
titanShifters.append("Colossal Titan")

Both do exactly the same thing. The second one is what you'll see most in the wild. 🌿

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🛠️ Useful Array Operations

📏 Count — How many items?

var surveyCorps = ["Eren", "Mikasa", "Armin", "Levi"]
print(surveyCorps.count) // 4

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🗑️ Remove Items

var titans = ["Attack", "Armored", "Colossal", "Beast", "War Hammer"]

titans.remove(at: 2)   // Removes "Colossal"
print(titans.count)    // 4

titans.removeAll()     // Wipes everything
print(titans.count)    // 0

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🔍 Check if Something Exists — contains()

let seasons = ["Season 1", "Season 2", "Season 3", "The Final Season"]
print(seasons.contains("Season 4"))          // false
print(seasons.contains("The Final Season"))  // true

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🔤 Sort Your Array — sorted()

let characters = ["Reiner", "Annie", "Bertholdt", "Zeke"]
print(characters.sorted())
// ["Annie", "Bertholdt", "Reiner", "Zeke"]

sorted() returns a new sorted array — the original stays unchanged. Neat! ✨

For numbers, it sorts smallest → largest:

let episodes = [7, 1, 22, 13, 4]
print(episodes.sorted()) // [1, 4, 7, 13, 22]

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🔄 Reverse an Array — reversed()

let arcs = ["Trost", "Female Titan", "Clash of Titans", "Return to Shiganshina"]
let reversed = Array(arcs.reversed())
print(reversed)
// ["Return to Shiganshina", "Clash of Titans", "Female Titan", "Trost"]

💡 Pro tip: Swift doesn't actually rearrange the items when you call reversed(). It just remembers you want them reversed — lazy in the best possible way. Wrapping it in Array() gives you a plain array back.

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🧩 Putting It All Together

Here's a mini program using everything we covered:

// Starting lineup
var squadMembers = ["Eren", "Mikasa", "Armin"]

// Add more members
squadMembers.append("Levi")
squadMembers.append("Hange")

// Check the roster
print("Squad size: \(squadMembers.count)") // 5

// Is Zeke in the squad?
print(squadMembers.contains("Zeke")) // false

// Sort alphabetically
print(squadMembers.sorted())
// ["Armin", "Eren", "Hange", "Levi", "Mikasa"]

// Remove Eren (he went rogue 😬)
squadMembers.remove(at: 0)
print(squadMembers.count) // 4

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🧵 Quick Recap

Feature	What it does	Example
[]	Create an array	var names = ["A", "B"]
[0]	Access by index	names[0]
.append()	Add an item	names.append("C")
.count	Total items	names.count
.contains()	Check existence	names.contains("A")
.sorted()	Sort (new array)	names.sorted()
.reversed()	Reverse (new array)	names.reversed()
.remove(at:)	Remove by index	names.remove(at: 0)
.removeAll()	Wipe the array	names.removeAll()

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🎯 Why This Matters

Arrays are everywhere in real apps. Every list you see on screen — messages, contacts, search results, leaderboards — is backed by an array under the hood. Getting comfortable with them early is one of the best investments you can make as a Swift developer. 💪

Next up, we'll look at dictionaries — another way to store data, but with labels instead of positions. See you there! 👋

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