App Development with Swift - Lesson 13 - Exercise: "isBelow13" - swift3

Question

I'm pretty new to Swift and I learn by using the "App Development with Swift"-Book.
Could you please check the code below - it doesn't work and I can't figure out why.
import UIKit
func isBelow13(number: Int) -> Bool {
let isBelow: Bool = false
if number < 13 {
let isBelow = true
} else {
let isBelow = false
}
return isBelow
}
isBelow13(number: 11) // returns false, should return true
isBelow13(number: 14) // returns false
Cheerio!

Answer 1

You're defining isBelow as false first, then inside your if statements you're defining a new constant called isBelow. This new constant has the same name as the above one, but is actually totally different. When you're outside of your if statements that one you created inside the if statements doesn't exist anymore and it just returns the one you first created. You're not actually changing the first isBelow that you set initially at all.
What you're actually trying to do can be accomplished like this:
func isBelow13(number: Int) -> Bool {
var isBelow: Bool = false
if number < 13 {
isBelow = true
} else {
isBelow = false
}
return isBelow
}
isBelow13(number: 11) // returns true
isBelow13(number: 14) // returns false
This way you are creating a variable that can be re-assigned "var" instead of "let" and then you are changing the value of that variable based on the if statement condition. Then you're returning that changed value. Make sense?
A more concise version of the same above code would look like this: (From #MartinR in the comments)
func isBelow13(number: Int) -> Bool {
return number < 13
}
The expression number < 13 returns a boolean value so you can just return the result of that expression from your function.