how do I set CKEditor into a php?

ok, I changed the approach. Now:

echo 'Message: <br /><textarea id="post_content" name="post_content" /></textarea><br /><br />
<input type="submit" value="Create topic" />";

$ckeditor = new CKEditor();
$ckeditor->basePath = '/ckeditor/'; <-- line #69
$CKEditor->editor("post_content", "This is some sample text");

which results in:
Warning: Division by zero in /create_topic.php on line 69

files structure:
/posting/create_topic.php
/poting/ckeditor/