guard let สำหรับการออกก่อนกำหนด

func greet(_ name: String?) {
    guard let name else {
        print("No name")
        return
    }
    print("Hello, \(name)")
}
greet("Ada")
greet(nil)

func double(_ text: String) {
    guard let n = Int(text) else {
        print("Not a number")
        return
    }
    print(n * 2)
}
double("8")
double("x")

func length(of text: String?) {
    guard let text else { return }
    let count = text.count
    print(count)
}
length("hello")

func process(_ value: Int?) {
    guard let value else {
        return
    }
    print("Processing \(value)")
}
process(99)

func show(_ name: String?) {
    guard let name else {
        print("missing")
        return
    }
    print(name)
}
show("Kai")

func register(name: String?, age: Int?) {
    guard let name else { return }
    guard let age else { return }
    print("\(name) is \(age)")
}
register(name: "Mia", age: 28)

func divide(_ a: Int, by b: Int) {
    guard b != 0 else {
        print("Cannot divide by zero")
        return
    }
    print(a / b)
}
divide(10, by: 2)
divide(10, by: 0)

let inputs = ["1", "x", "3"]
for item in inputs {
    guard let n = Int(item) else { continue }
    print(n * 10)
}

func combine(_ a: String?, _ b: String?) {
    guard let a, let b else { return }
    print(a + b)
}
combine("foo", "bar")

func validate(_ text: String?) {
    guard let text, !text.isEmpty else {
        print("invalid")
        return
    }
    print("ok: \(text)")
}
validate("")
validate("hi")

func area(width: Int?, height: Int?) -> Int {
    guard let width, let height else { return 0 }
    return width * height
}
print(area(width: 3, height: 4))

func f(_ x: Int?) {
    guard let x else { return }
    print(x)
}
f(5)