Swift — Loops

For loop

// Closed range
for i in 1...5 {
    print(i, terminator: " ")
}
print() // 1 2 3 4 5

// Half-open range
for i in 0..<5 {
    print(i, terminator: " ")
}
print() // 0 1 2 3 4

// Stride
for i in stride(from: 0, to: 10, by: 2) {
    print(i, terminator: " ")
}
print() // 0 2 4 6 8

Iterating collections

let nums = [1, 2, 3, 4, 5]

for num in nums {
    print(num, terminator: " ")
}
print()

// With index
for (index, num) in nums.enumerated() {
    print("\(index): \(num)")
}

Iterating strings

let word = "Hello"

for char in word {
    print(char, terminator: " ")
}
print() // H e l l o

Iterating dictionaries

let ages = ["Alice": 30, "Bob": 25]

for (name, age) in ages {
    print("\(name): \(age)")
}

While loop

var count = 0
while count < 5 {
    print(count, terminator: " ")
    count += 1
}
print() // 0 1 2 3 4

Repeat-while loop

var count = 0
repeat {
    print(count, terminator: " ")
    count += 1
} while count < 5
print() // 0 1 2 3 4

Labeled statements

outer: for i in 1...5 {
    for j in 1...5 {
        if i * j > 10 {
            break outer
        }
        print("(\(i),\(j))", terminator: " ")
    }
    print()
}

Mini Practice

Write Swift code that:

1. Uses stride to iterate with custom step
2. Enumerates a collection with index
3. Uses repeat-while for a menu loop
4. Uses labeled break to exit nested loops

Up Next

In the next lesson, you'll learn about Functions — defining and using functions in Swift.