title: Traverse using macros in STL
body: <pre><code>#include&lt;iostream&gt;
  #include&lt;string&gt;
  #include&lt;map&gt;
  using namespace std;
  int main()
  {
      map&lt;string, int&gt; M; 
      int r = 0; 
      tr(M, it) //this line is causing trouble
      { 
          r += it-&gt;second; 
      }  
  }
  </code></pre>
  
  <p>What header file or preprocessor command do I need to enter to run.</p>