title: Convert List<int> to string of comma separated values
body: <p>having a <code>List&lt;int&gt;</code> of integers (for example: <code>1 - 3 - 4</code>)
  how can I convert it in a string of this type?</p>
  
  <p>For example, the output should be:</p>
  
  <pre><code>string values = "1,3,4";
  </code></pre>