How to sum group of elements without for-loop and while(do-while) loops?

Question

How you will sum?
In this way you can sum group of elements without using for-loop writing on c++17 standard.
Try it for yourself:
https://code.sololearn.com/c2Ba6WX57Z0U/#cpp
Write your code using favorite language.

Answer 1

You can use while or do while

Answer 2

Good I should ask without for-loop and while-loops))