title: Regex in C# , Expression in negative lookbehind
body: <p>I`m trying to write an expression to match a single quote preceded by an odd number of question marks.</p>
  <p>I have found a negative look-behind expression to match a single question mark</p>
  <pre><code>pattern (?&lt;!\?)'
  
  aaa?'aaa   match
  aaa'aaaa   not match
  aaa??'aaa  match --wrong
  </code></pre>
  <p>But what I need is to detect an odd number of question marks, not just one.<br />
  I tried to put it like <code>(?&lt;!\?(??))'</code> but it did not work.</p>
  <p>The result I want is</p>
  <pre><code>aaa?'aaaa  match
  aaa??'aaaa  not match
  aaa???'aaaa  match
  aaa????'aaaa  not match
  aaa?????'aaaa  match
  </code></pre>