Reading Input in Swift

Last year’s programs read their input in Python. Swift reads a line the same way, with one difference worth meeting early: readLine() might give back nothing at all, so Swift makes you say what to do then.

Ask, then answer

Type your name and your age on two lines of the input box under the program, then press Run.

print("What is your name?")
let name = readLine() ?? ""
print("How old are you?")
let ageText = readLine() ?? ""
 
if let age = Int(ageText) {
    print("Hello, \(name)! Next year you will be \(age + 1).")
} else {
    print("Hello, \(name)! \"\(ageText)\" is not a whole number.")
}

Then try it with an age written as a word. Which line of the program decides what happens?

What to notice

• readLine() ?? "" turns “nothing at all” into an empty string, so the rest of the program only ever deals with text.
• Int(ageText) might fail, so it gives back an optional; if let runs its block only when the text really was a whole number.