title: C++ nested iterator on the same map?
body: <p>for example in Array:
  I can do </p>
  
  <pre><code>for (int i =0; i &lt; array.size(); i++) {
      for (int j =i; j &lt; array.size(); j++) {
          do something 
     }
  }
  </code></pre>
  
  <p>how do I do such nested style for C++ map:</p>
  
  <pre><code>for (auto it = map.begin(); it != map.end(); ++it) {
      for (auto lt = it;  lt != map.end(); ++lt) {
      dosomething.
     }
  }
  </code></pre>
  
  <p>am I doing right for the c++ map ?</p>