Swift Loops — while, repeat and Knowing When to Use Each 🔄

Source: Dev.to

In our last article we covered for loops — perfect for when you know exactly how many times you need to repeat something. But what happens when you don’t know how many times you’ll need to loop?

That’s where while and repeat loops come in. 🧠

🔄 The While Loop — Run Until a Condition Is False

A while loop keeps running as long as a condition is true. The moment the condition becomes false, the loop stops:

while someCondition {
    // code to repeat
}

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No array needed. No range needed. Just a condition. Let’s see it in action:

var countdown = 10

while countdown > 0 {
    print("\(countdown)...")
    countdown -= 1
}

print("Blast off! 🚀")

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Output:

10...
9...
8...
7...
6...
5...
4...
3...
2...
1...
Blast off! 🚀

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Breaking it down:

We start with countdown = 10

• The loop checks countdown > 0 before every iteration

• Inside the loop we print the number and subtract 1

• When countdown hits 0 the condition becomes false and the loop stops

• The final message prints after the loop ends

  🎲 Random Numbers + While Loops — A Perfect Combo

Here’s where while loops really shine — when you genuinely don’t know how many times you’ll need to loop.

Swift gives us a fantastic tool called random(in:) that generates a random number within a range:

let id = Int.random(in: 1...1000)        // random Int between 1 and 1000
let amount = Double.random(in: 0...1)    // random Double between 0 and 1

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Now let’s combine this with a while loop. Imagine you’re playing a game and need to keep rolling a dice until you land a critical hit — a 20 on a 20-sided dice:

var roll = 0

while roll != 20 {
    roll = Int.random(in: 1...20)
    print("Rolled: \(roll)")
}

print("Critical hit! ⚔️")

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Output (will vary every time):

Rolled: 7
Rolled: 13
Rolled: 4
Rolled: 19
Rolled: 20
Critical hit! ⚔️

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Every time you run this code you’ll get a different result — sometimes lucky, sometimes not. This is impossible to replicate cleanly with a for loop because you simply don’t know how many rolls it will take. That’s the whole point of while. 🎯

🎮 Another Example — Grinding for Power

Let’s say you’re building an RPG and a character needs to keep training until their power level hits 9000:

var powerLevel = 1
var trainingRounds = 0

while powerLevel  0 && bossHealth > 0 {
    let playerDamage = Int.random(in: 10...30)
    let bossDamage = Int.random(in: 5...20)

    bossHealth -= playerDamage
    health -= bossDamage

    print("Round \(round):")
    print("  You dealt \(playerDamage) — Boss health: \(max(0, bossHealth))")
    print("  Boss dealt \(bossDamage) — Your health: \(max(0, health))")
    print()

    round += 1
}

if health > 0 {
    print("🏆 You won in \(round - 1) rounds!")
} else {
    print("💀 Defeated in \(round - 1) rounds. Try again!")
}

// Repeat loop — generate a unique reward code
let usedCodes = [1111, 2222, 3333]
var rewardCode: Int

repeat {
    rewardCode = Int.random(in: 1000...9999)
} while usedCodes.contains(rewardCode)

print("🎁 Your reward code: \(rewardCode)")

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🌟 Wrap Up

Now you know all three loop types in Swift:

for — when you know exactly how many times to loop

while — when you loop until a condition becomes false, checked before each run

repeat — when you always need at least one run, condition checked after

And remember — always make sure your while or repeat condition will eventually become false, or you’ll end up with an infinite loop! 🔒

Next up we’ll look at how to skip loop iterations and exit loops early using continue and break. See you there! 👋