title: Why we use -'0' beside charAt(i)?
body: <p>I read Hello Android book and i dont understand a piece of code this function.</p>
  
  <p>Why we use -'0' beside charAt(i)??</p>
  
  <pre><code>static protected int[] fromPuzzleString(String string) {
      int[] puz = new int[string.length()];
      for (int i = 0; i &lt; puz.length; i++) {
          puz[i] = string.charAt(i) - '0' ;
      }
      return puz; 
   }
  </code></pre>
  
  <p>Thanks you.
  Cheers.</p>