title: unordered_map::find() inserts the key of the lookup
body: <p>Is it a feature of unordered_map::find() to insert the key that we lookup with 0 value automatically?
  Let me make this clear</p>
  
  <pre><code>    unordered_map&lt;int, int&gt; tempMap;
      //some code
      if(tempMap.find(1) == tempMap.end()){
        //do something but not insert the 1 with a corresponding value into the tempMap
      }
  </code></pre>
  
  <p>so if I lookup 1 again, will it be there in the tempMap having 0 as corresponding value.
  Is that a feature of unordered_map?</p>