Performance issue for vector::size() in a loop in C++

Question

In the following code:

std::vector var;
for (int i = 0; i < var.size(); i++);

Is the

Answer 1

It's 'called' each time, but I put called into quotes because it really probably is just an inline method call, so you don't have to worry about its performance.

Why not use vector::iterator instead?