Control Flow

Swift provides a variety of control flow statements including conditionals, loops, and early exits. This lesson covers if, guard, switch, for-in, while, and control transfer statements.

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If Statements

let temperature = 25

if temperature > 30 {
    print("It's hot!")
} else if temperature > 20 {
    print("It's pleasant.")
} else {
    print("It's cool.")
}

Note: Conditions in Swift must be Bool expressions. Unlike C or JavaScript, there is no implicit conversion from numbers to booleans.

If Expressions (Swift 5.9+)

let mood = if temperature > 25 { "warm" } else { "cool" }

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Guard Statements

guard provides an early exit when a condition is not met:

func greet(name: String?) {
    guard let name = name else {
        print("No name provided.")
        return
    }
    // 'name' is now a non-optional String
    print("Hello, \(name)!")
}

Best Practice: Use guard for preconditions at the top of a function. The happy path stays unindented, making code easier to read.

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Switch Statements

Swift's switch is powerful and exhaustive:

let grade = "A"