title: How to modify value in unorderedmap?
body: <p>I would like to try inserting an element into the map with key k and value v. If the key is already present, I want to increment the value of that key.</p>
  
  <p>Example,</p>
  
  <pre><code>typedef std::unordered_map&lt;std::string,int&gt; MYMAP;
  
  MYMAP mymap;
  std::pair&lt;MYMAP::iterator, bool&gt; pa=  
      mymap.insert(MYMAP::value_type("a", 1));
  if (!pa.second)
  {
      pa.first-&gt;second++;
  } 
  </code></pre>
  
  <p>This does not work. How can I do this?</p>