shorter notation for size_type in std::vectors

When iterating over a std::vector, I've always declared the index variable to be of size_type as in

std::vector<someReallyLengthy<TypeWith,SubTypes>> a(5);
for (std::vector<someReallyLengthy<TypeWith,SubTypes>>::size_type k = 0; k < a.size(); k++) {
  // do something with a[k]
}

I'm wondering if in C++11 (or later) there's a shorthand-notation for the size_type here.

(auto won't work since it can't deduct from 0 which type it targets.)