title: CheckedListBox and list of checked items with their indexes
body: <p>I have a <code>CheckedListBox</code> like this:</p>
  
  <pre><code>:'''''''''''''''/\
  : [ ] item1     ||
  : [x] item2     ||
  : [ ] item3     ##
  : [ ] item4     ||
  : [x] item5     ||
  L...............\/
  </code></pre>
  
  <p>Now I want to extract indexes of checked items:  </p>
  
  <pre><code>int[] indexes = ExtractCheckedIndexes (myCheckedListBox);
  </code></pre>
  
  <p>Now indexes should have 2 elements = { 1, 4 }.<br>
  How to achieve this?</p>