retain state with radio buttons and checkboxes

I looked everywhere in the forums and can't find an answer to how I would retain the value of a radio button, or a checkbox using set_radio() or set_checkbox() after a form is submitted. I also tried all sorts of ways of inserting set_radio() and set_checkbox(). What syntax should I use in the code below?

Example:

PHP Code:

<div class="form-control">
     Client has read and understood the confidentiality guidelines.
 <?php 
    $data = array(
 'name'  => 'guidelines',
 'id' => 'signed_yes',
 'value' => 'yes',
 'style' => 'margin-left: 20px;'
 );
    echo form_radio($data); 
 ?>
 <?php echo form_label('Yes', 'signed_yes'); ?>
 <?php 
 $data = array(
 'name'  => 'guidelines',
 'id' => 'signed_no',
 'value' => 'no',
 'checked' => TRUE,   // default value
 'style' => 'margin-left: 20px;'
 );
 echo form_radio($data); 
 ?>
 <?php echo form_label('No', 'signed_no'); ?>
 </div><!-- end of .form-control -->
        <div class="form-control">
 A signed confidentiality guideline is on file for this client.
 <?php 
 $data = array(
 'name'  => 'guidelines_signed',
 'value' => 'yes',
 'style' => 'margin-left: 20px;'
 );
 echo form_checkbox($data)); 
 ?>
 </div><!-- end of .form-control -->