title: error when trasforming tolower, help would be nice
body: <p>I'm trying to convert a txt file so all words can be lower case. and when I try I get an error I've tried to differ ways but no luck, my code is as followed </p>
  
  <pre><code>              ifstream words("sample_doc.txt"); 
                ofstream samp("sample.txt");
                set &lt;string&gt; lower;
                set &lt;string&gt; to_low;
  
                copy(istream_iterator&lt;string&gt;(words), istream_iterator&lt;string&gt; (), inserter(lower, begin(lower)) );
  
                transform(begin(lower), end(lower), inserter(to_low, begin(to_low) ), tolower ); 
  </code></pre>
  
  <p>when I tried to complete I get this error<br>
  'int (int)': cannot convert argument 1 from 'const std::basic_string,std::allocator>' to 'int'    </p>