Question

What advantages are there in accessing vector elements using an iterator vs an index?

Answer 1

Why are iterators better than indexes?

• In the cases where index is not available (like with std::list, for
  example).
• In the case where a generic function accepting an iterator
  is called.
• When writing a function template that is supposed to work with
  more than one container type.
• They exist to create uniformity among all containers and ability to use
  all containers’ iterators as well as regular pointers in all standard
  algorithms.
• Iterators can point to sequences that don’t exist except as a concept.
  For instance, you can make an iterator class that steps through prime
  numbers without actually having to build a container of primes.

However, if ignoring container types that do not support random access (list, set, etc.), iterators still offer

• Pointer like semantics (think of string::iterator vs. char *).
• Generalized concept usable beyond iteration over elements inside a
  container.
• Better performance than container member functions in a few cases.