title: codeigniter form validation for checkbox at least one selection
body: <p>I know how to make a form validation for each of inputs in codeigniter. But is it possible to make a validation for multiple checkbox where the user should select at least one check box?</p>
  
  <p>example</p>
  
  <pre><code>&lt;input type=checkbox name=days[] &gt;Mon
  &lt;input type=checkbox name=days[] &gt;Tues
  &lt;input type=checkbox name=days[] &gt;Wed
  &lt;input type=checkbox name=days[] &gt;Thur
  </code></pre>
  
  <p>where the codeigniter should validate that the user should select at least one checkbox.? </p>