title: using string format for a credit card number
body: <p>I'm trying to display a credit card number as a string like #### #### #### ####</p>
  
  <p>I tried:</p>
  
  <pre><code>txtbox.Text = string.Format("{0:#### #### #### ####}", ccNumber);
  </code></pre>
  
  <p>and it didn't work.  Any ideas?</p>