Prefer to terminate `std::cout` with `<< std::endl;` rather than `\n`

[ASmoliak]

When streaming newlines, it is a good idea to terminate with << std::endl
it's easier to maintain and understand, you can easily miss adding a \n when you have a large amount of output.
It will also flush every line, while it can hurt performance, if you wanted performance you wouldn't use std::cout anyway.

[yonicswe]

done