Hi,

You are right. It would be good practice to have something but maybe not a return. The only way to finish the loop is if the input is invalid (e.g. no missing letter). The kata doesn't define what should happen (e.g. there isn't a special error character to return). Maybe throwing an exception would be appropriate.

Good implementation, but you should use std::isalpha instead of the 'a','z' check.

Shouldn't you have a last return instruction ? Does it work without it ?...

Shouldn't you have a last return instruction ?

Instead of the break instruction you could have put the return instruction directly.

This seems like recursive-math thinking to me; and translating it into code is trivial. It's the base for dynamic-programming algorithms, I think.
:(, I personally never caught this math thinking skill. But it's great, inspiring; if I see some more of these, I may be able to catch this thinking-technique myself :).