SW Swift

Swift: Control Flow

What you will learn

Conditionals, Swift's powerful switch statement, and the for-in loop with ranges.

if / else if / else

let score = 85
if score >= 90 {
    print("A")
} else if score >= 80 {
    print("B")
} else {
    print("F")
}

Conditions must be boolean — no truthy/falsy coercion.

For-in with ranges

for i in 1...5 {
    print(i)  // 1, 2, 3, 4, 5
}

for i in 1..<5 {
    print(i)  // 1, 2, 3, 4 (half-open, excludes 5)
}

for char in "Hello" {
    print(char)  // H e l l o
}

... is the closed range operator (includes both ends). ..< is the half-open range operator (excludes the last value).

Switch statement

Swift's switch is exhaustive — every possible value must be covered:

let day = "Monday"
switch day {
case "Monday":
    print("Start of week")
case "Friday":
    print("Almost weekend")
default:
    print("Midweek")
}

No break needed — Swift's switch does not fall through. Use fallthrough explicitly if you want C-style fallthrough.

While loops

var i = 0
while i < 5 {
    print(i)
    i += 1
}

Guard statement (Swift's unique early exit)

guard is like an if that requires an else to exit the current scope. It keeps the "happy path" unindented:

func greet(person: [String: String]) {
    guard let name = person["name"] else {
        return  // name was nil — exit early
    }
    print("Hello, \(name)!")  // happy path
}

Common mistakes

  • Forgetting a default case in switch — Swift requires exhaustive coverage
  • Using ... when you meant ..< — off-by-one bugs are common with ranges
  • Expecting if to accept non-boolean values — Swift only accepts true Bool expressions

Quick check below!

Next: Functions & Closures