title: C# Matching letters, numbers and special character in regex
body: <p>I have the following <code>Regex</code>:</p>
  
  <pre><code>[A-Z]{2}[0-9]{4}
  </code></pre>
  
  <p>and it matches perfectly with a string like this: <code>AB1234</code>. But I have to improve this <code>Regex</code> to match with these specific rules:</p>
  
  <ul>
  <li>The string must have only <strong>two</strong> sharps (##) between each group (<code>AB1234##AB1234</code>)</li>
  <li>It may have 8 groups of string (<code>AB1234##AB1234##AB1234##AB1234##AB1234##AB1234##AB1234##AB1234</code>)</li>
  <li>Regardless the number of groups, the last one cannot have the sharps (##) at the end. So, if I have 3 groups, it will looks like this: <code>AB1234##AB1234##AB1234</code></li>
  </ul>
  
  <p>If I use the sample string from the second bullet point, my <code>Regex</code> will match with the pattern, but in this case it doesn't validade the characters between each group.</p>
  
  <p>Can anyone help me to improve this Regex?</p>