title: How to self-copy a vector?
body: <p>Let's say I have a <code>vector&lt;string&gt;</code> containing "a" and "b", I wanna copy itself 2 times so that the vector now contains "a", "b", "a", "b", "a", "b"</p>
  
  <p>What is a better approach than using <code>for</code> and <code>push_back</code>?</p>