The binary?! Smart

you dont need two semicolons, the second one is doing literally nothing

you can do stuff like this too:

int a = 5;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

i did the same

yep. Return {0,0}

@KirinCupr: just a quick confirmation - you're completely right, the creator of the Kata has defined "input_str" as a constant here, so while we can read its value, we must not change/manipulate it! ... The C++ documentation says about the use of the keyword "const": "an object whose type is 'const-qualified', or a non-mutable subobject of a const object. Such object cannot be modified: attempt to do so directly is a compile-time error ..."

Hello. I'm think we create new variable because "input_str" is is const (const std::string& input_str). So we can't change it. If I'm wrong, please, correct me.

what all these functions ??

well done!

This is incorrect. And it is exactly why it is better not to skip it.

Classic

MOD is normally compiled as IMUL, a very expensive operation (consider using & instead).
At a conceptual level, there is no need to introduce branching with operator ?. Consider an array subindex.