XCode Playground (Swift) 中的递归函数

Question

I'm learning recursive functions in Swift, and I did the following:

func recursive(i: Int) -> Int {
    if i == 1 {
        return 1
    } else if i >= 2 {
        return recursive(i: i - 1) + 1
    }
    return 0
}

I couldn't figure out why the function above is not working. I've tested it by doing the below doing print(recursive(10)) , which gives me an output of 10. I expected the output to be 1. Can anyone help me with this? Thank you in advance.

I'm using Playgrounds on XCode 8.3.

Answer 1

When you do this:

recursive(i: i - 1) + 1

… then you are in effect decrementing i and then incrementing it again. That cancels out and you arrive at i again.

Let's write down what calculation would be done for i = 3 :

(3 - 1) + 1 = ((2 - 1) + 1) + 1 = (((1) + 1) + 1) = 3

Answer 2

This is a perfect example of printing numbers without using any loop.

The recursive functions are very useful to handle such cases.

func printCount( count : inout Int , limit : Int) {
    
    print(count, terminator: " ")
    count += 1  
    if count  > limit {
        return
    }
    
    printCount(count: &count , limit: limit)
}

var count = 11
let limit = 20
printCount(count: &count , limit: limit)

Output : 11 12 13 14 15 16 17 18 19 20