title: Convert text in an NSString to it's 8-byte ASCII Hex equivalent, and store back in an NSString
body: <p>I want to convert the NSString <code>@"2525"</code> to the NSString <code>@"0032003500320035"</code>.  The 8-byte ASCII value for <code>"2"</code> in hex is <code>"0032"</code> and for <code>"5"</code> it's <code>"0035"</code>.  Just to get the c-string equivalent, I tried...</p>
  
  <pre><code>const char *pinUTF8 = [pin cStringUsingEncoding:NSASCIIStringEncoding];
  </code></pre>
  
  <p>...but as you can see I'm struggling with this and I knew it wasn't going to be that easy.  Any tips?</p>
  
  <p>Thanks so much in advance for your wisdom!</p>