title: What is 'long?' data type?
body: <p>I am going over some code written by another developer and am not sure what <code>long?</code> means:</p>
  
  <pre><code>protected string AccountToLogin(long? id)
  {
     string loginName = "";
     if (id.HasValue)
     {
        try
        {....
  </code></pre>