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Swift Academy · Lesson

Closed and Half-Open Ranges

Use ... and ..< correctly in loops and slices.

Lesson 1 of 413 steps

Closed and Half-Open Ranges is a free Swift Academy lesson on CoddyKit. This is lesson 1 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, and your progress syncs across the web and the CoddyKit app. The Swift Academy course includes 4 lessons in total.

What Is a Range

A range represents a sequence of values between a lower and upper bound. Swift has two main range operators for this.

let r = 1...5
for n in r {
    print(n)
}

Closed Range

The closed range operator a...b includes both endpoints. 1...5 contains 1, 2, 3, 4, and 5.

for n in 1...5 {
    print(n)
}

Half-Open Range

The half-open range operator a..<b includes the lower bound but excludes the upper. 0..<5 contains 0, 1, 2, 3, 4.

for n in 0..<5 {
    print(n)
}

Why Half-Open Is Common

Half-open ranges pair perfectly with counts and indices. 0..<array.count visits every valid index exactly once.

let items = ["a", "b", "c"]
for i in 0..<items.count {
    print("\(i): \(items[i])")
}

Ranges Have a count

A range knows how many values it spans via its count property.

let closed = 1...5
let halfOpen = 0..<5
print(closed.count)
print(halfOpen.count)

Checking Membership

Use contains to test whether a value lies within a range.

let valid = 1...100
print(valid.contains(50))
print(valid.contains(0))
print(valid.contains(101))

Lower and Upper Bounds

Every range exposes lowerBound and upperBound properties.

let r = 10...20
print(r.lowerBound)
print(r.upperBound)

Empty and Single Ranges

A half-open range like 5..<5 is empty. A closed range cannot be empty because both ends are included.

let empty = 5..<5
print(empty.isEmpty)
let single = 5...5
print(single.count)

Ranges in switch

Ranges work as switch case patterns to classify a value into buckets.

let score = 73
switch score {
case 0..<60:
    print("Fail")
case 60...100:
    print("Pass")
default:
    print("Invalid")
}

Bounds Must Be Ordered

The lower bound must not exceed the upper bound. Writing 5...1 crashes at runtime, so keep bounds in order.

let lo = 2
let hi = 8
if lo <= hi {
    for n in lo...hi {
        print(n)
    }
}

Counting Iterations

When you only need to repeat something N times and ignore the index, use a range with _.

var total = 0
for _ in 1...4 {
    total += 10
}
print(total)

Quick Check

Test closed vs half-open ranges.

Answer it in the interactive lesson

Recap: Closed and Half-Open Ranges

a...b includes both ends; a..<b excludes the upper end and pairs naturally with counts and indices. Ranges support count, contains, and bound properties.

for i in 0..<3 { print(i) }
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Frequently Asked Questions

Is the “Closed and Half-Open Ranges” lesson free?

Yes — any 3 lessons of the Swift Academy learning path, including “Closed and Half-Open Ranges”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Swift Academy course includes 4 lessons in total.

What will I learn in “Closed and Half-Open Ranges”?

Use ... and ..< correctly in loops and slices. You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Swift Academy?

No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “Closed and Half-Open Ranges” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Swift Academy lesson?

Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Closed and Half-Open Ranges
  2. One-Sided Ranges
  3. Counting with stride(from:to:by:)
  4. Ranges as Collections
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