you should only use & in a for loop if you intend to modify the element

Not really. In general you should always access the element by reference (i.e. " &x" if you need to modify it, or "const &x" if you don't), otherwise C++ must make a copy into the loop varible. HOWEVER, in the case of a built-in type like int, just getting a copy is (almost?) always just as efficient or more efficent that getting the elements address and then deref'ing it.

Thank you. We can still do without it anyway, no big deal.

That'd be impossible to be implement.

No. But you can make a suggestion on CW github by raising an issue about it.

I was just comparing perfomances of the submitted solutions and most of "best practices" are really slow. I suggest that the algorithm that lists the solutions should use perfomance as a metric.