form validation, set_value and initial value

You are wrong  

In the docs:
https://www.codeigniter.com/user_guide/h...#set_value

You would set a value like this:

PHP Code:

<input type="text" name="quantity" value="<?php echo set_value('quantity', '26'); ?>" size="50" /> 


This would set a default value of 26 to the input field.

I hope that helps,

Paul

PS The docs are excellent - they are worth reading in detail.