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Swift Academy · Lesson

for-in Loops with Ranges

Iterating with for-in using integer ranges and closed/half-open range operators.

Lesson 1 of 412 steps

for-in Loops with 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.

Welcome

Loops let you repeat work without repeating code. The `for-in` loop is Swift's most versatile iteration tool, working with ranges, collections, and any sequence.

Closed Range: a...b

The closed range operator `...` includes both endpoints: ```swift for i in 1...5 { print(i) // 1, 2, 3, 4, 5 } ``` This is the most common range used with `for-in`.

Half-Open Range: a..<b

The half-open range `..<` excludes the upper bound — perfect for 0-based indexing: ```swift for i in 0..<5 { print(i) // 0, 1, 2, 3, 4 } ``` Useful when iterating array indices: `0..

One-Sided Ranges

One-sided ranges extend to one end: ```swift let nums = [10, 20, 30, 40, 50] for n in nums[2...] { print(n) } // 30, 40, 50 for n in nums[..<3] { print(n) } // 10, 20, 30 ``` Very handy when slicing collections from/to a position.

stride(from:to:by:)

Use `stride` when you need a custom step size: ```swift for i in stride(from: 0, to: 10, by: 2) { print(i) // 0, 2, 4, 6, 8 } for i in stride(from: 10, through: 0, by: -3) { print(i) // 10, 7, 4, 1 } ```

Ignoring the Loop Variable

Use `_` when you don't need the iteration value: ```swift var sum = 0 for _ in 1...10 { sum += 1 } print(sum) // 10 ``` This signals to readers that the count matters, not the index.

Iterating Characters in a String

Strings conform to `Sequence`, so you can iterate characters directly: ```swift for char in "Swift" { print(char) // S, w, i, f, t } ``` Each `char` is of type `Character`.

Ranges as Values

Ranges are first-class Swift values and can be stored: ```swift let valid: ClosedRange = 1...100 if valid.contains(42) { print("In range") } ``` Useful for validation and switch case matching.

Nested for-in Loops

Loops can be nested for multi-dimensional iteration: ```swift for row in 1...3 { for col in 1...3 { print("(\(row),\(col))", terminator: " ") } print() } ``` Watch out for O(n²) complexity when nesting deep.

Counting Down with Reversed

Reverse a range with `.reversed()`: ```swift for i in (1...5).reversed() { print(i) // 5, 4, 3, 2, 1 } ``` Alternatively use `stride(from:through:by:)` with a negative step.

Quick Check

Which range operator **excludes** the upper bound?
Answer it in the interactive lesson

Recap

Key takeaways: • `a...b` — closed range (includes b) • `a..
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Frequently Asked Questions

Is the “for-in Loops with Ranges” lesson free?

Yes — any 3 lessons of the Swift Academy learning path, including “for-in Loops with 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 “for-in Loops with Ranges”?

Iterating with for-in using integer ranges and closed/half-open range operators. 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 “for-in Loops with 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. for-in Loops with Ranges
  2. while and repeat-while Loops
  3. Iterating Collections with for-in
  4. break, continue and Labeled Statements
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