c++ uint , unsigned int , int

C++ defines no such type as uint. This must be “your” type, i.e. a type defined in your code or some third party library. One can guess that it is the same as unsigned int. Could be unsigned long int though or something else. Anyway, you have to check it yourself.

It is a matter of personal style. I, for example, believe that one has to use unsigned types to represent naturally non-negative values, like sizes or quantities. There’s no difference in performance between signed and unsigned types, aside from some specific contexts. I would say that in most cases it is unsigned types that will be handled more efficiently.

Iterators make implementations more generic, i.e. you can use sequential-access iterator and thus make your implementation applicable to any sequential data structure. By using index you impose the random-access requirement on the data structure, which is a strong requirement. It is not a good idea to impose strong requirements when there’s no real need for them.