Loops

Enemy 1 of 5

Loops let you repeat a block of code without writing it out by hand every time. Swift's for loop walks over a range of values: for i in 0..<3 { ... } runs its body three times, with i taking the values 0, then 1, then 2 in turn.

The ..< operator is a half-open range: it includes the starting value (0) but excludes the ending value (3). This matches Rust's 0..3 exactly, and it's genuinely convenient once it clicks — the number of iterations is simply the end minus the start, with no mental "plus or minus one" adjustment needed. Swift also has a fully closed range operator, ... (three dots, no less-than sign), which includes both ends: 1...5 covers 1, 2, 3, 4, and 5. Mixing up ..< and ... is a classic source of off-by-one bugs, so pay close attention to which one a piece of code uses.

Compared to a classic C-style for (int i = 0; i < 3; i++) loop, Swift's for i in 0..<3 reads closer to plain English, and there's no separate condition or increment step to get wrong — the range fully describes what values i will take.