if let

var a : Int? = 100

var b : Int? = nil

 

if let num = a {

    print("num = \(num)")

} else {

    print("num is nil")

}

// result : num = 100

 

if let num = b {

    print("num = \(num)")

} else {

    print("num is nil")

}

// result : num is nil

 

if var num = a {

    num *= 2

    print("num = \(num)")

} else {

    print("num is nil")

}

// result : num = 200