# Recursion (count)

``````function countup(n) {
if (n < 1) {
return [];
} else {
const countArray = countup(n - 1);
countArray.push(n);
return countArray;
}
}
console.log(countup(5));
``````

Please I don’t understand how this returns [1,2,3,4,5] instead of [4,3,2,1] as I am thinking cos the number ’ n ‘ ought to be decreasing (n-1)

Two questions for you to think about

1. What is `countup(4)` supposed to return

2. What happens if you push 5 onto that result

I still don’t understand this. Please Can you explain the code in your own words. Thanks

The logic please using n = 5. Thank you

I understand that the code may seem confusing at first. Let’s break it down step by step.

The `countup` function takes a parameter `n` and returns an array of numbers starting from 1 up to `n`.

Here’s how it works:

1. When `countup` is called with a value of `n`, it checks if `n` is less than 1 (`n < 1`).
2. If `n` is less than 1, it means we’ve reached the base case, and the function returns an empty array `[]`.
3. If `n` is not less than 1, it means we need to continue counting up.
4. In this case, the function recursively calls itself with `n - 1` as the argument: `countArray = countup(n - 1)`.
5. The recursive call will continue until it reaches the base case, where `n` is less than 1.
6. Once the base case is reached, the recursive calls start returning, and each call adds its respective `n` value to the `countArray`.
7. Finally, the function returns the `countArray`, which now contains all the numbers from 1 to `n` in ascending order.

So, when you call `countup(5)`, it goes through the recursive calls as follows:

1. `countup(5)` calls `countup(4)`
2. `countup(4)` calls `countup(3)`
3. `countup(3)` calls `countup(2)`
4. `countup(2)` calls `countup(1)`
5. `countup(1)` returns an empty array `[]`
6. `countup(2)` adds `2` to the array and returns `[2]`
7. `countup(3)` adds `3` to the array `[2]` and returns `[2, 3]`
8. `countup(4)` adds `4` to the array `[2, 3]` and returns `[2, 3, 4]`
9. `countup(5)` adds `5` to the array `[2, 3, 4]` and returns `[2, 3, 4, 5]`

That’s why the output is `[1, 2, 3, 4, 5]` instead of `[4, 3, 2, 1]`.

I hope this explanation helps clarify how the code works. If you have any more questions, feel free to ask!

Just the explanation I needed. I’m immensely grateful. Thank you very much. I now understand the logic

Thanks you. I think I’ve understood it

Thank you. I think I’ve understood it. I’m grateful

This topic was automatically closed 182 days after the last reply. New replies are no longer allowed.