Where do I create PHPTemplate variables in Drupal theming?

Here’s some code, which you can put into your template.php file. It demonstrates how to insert code into that file, so you can make new variables available to page, node and comment template files. Examples of where this is useful are shown in the snippet below.

<?php
function _phptemplate_variables($hook, $vars = array()) {
  switch ($hook) {
    case 'page':
      // code relating to variables for page templates here
      // EXAMPLE - is the current user logged in?
      $vars['logged_in'] = ($user->uid > 0) ? TRUE : FALSE;
      break;

    case 'node':
      // code relating to variables for node templates here
      // EXAMPLE - on front page teasers, make a comment count var using a query
      if ($vars['teaser'] && $vars['is_front']) {
        $vars['comment_count'] = db_result(db_query("SELECT comment_count 
          from {node_comment_statistics} where nid = %d", $node->nid));
      }

      break;

    case 'comment':
      // code relating to variables for comment templates here
      break;
  }
  // anything that you require for all the above, put outside the switch statement
  return $vars; // this passes the variables back to the relevant template
}
?>