In the unwrapping optional with guard lesson we are given this example:

func printSquare(of number: Int?) {
    guard let number = number else {
            print("missing input")
            return
    }

    print("\(number) x \(number) is \(number * number)")
}

If we run the function:

printSquare(of: 4)

4 x 4 = 16 is printed

In what circumstance will "missing input" be printed?

Thank you

Any circumstance in which number == nil

So, for instance:

printSquare(of: nil)
printSquare(of: Int("five"))

I see. Thank you!