title: c# pad left to string
body: <p>i want to find a efficent way to do :</p>
  
  <p>i have a string like :</p>
  
  <pre><code>'1,2,5,11,33'
  </code></pre>
  
  <p>i want to pad zero only to the numbers that below 10 (have one digit)</p>
  
  <p>so i want to get</p>
  
  <pre><code>'01,02,05,11,33'
  </code></pre>
  
  <p>thanks</p>