title: DateTime formats C#
body: <p>I have a string which needs to be converted and validated to a DateTime. The string is in the following format 'dd.mm.yy'
  I am trying to convert it to DateTime using the following </p>
  
  <pre><code>string format = "dd.mm.yy";
  date = DateTime.ParseExact(current.Substring(aiRule.AiLength), format, 
                                             CultureInfo.InvariantCulture);
  </code></pre>
  
  <p>but unfortunately this fails. 
  The question is how to convert a string in the format 'dd.mm.yy' to a DateTime ?
  Thank you</p>