[TYPO3] Form datavalidation

[rocky Ou]

Hey List,

I'm writting an Extension which collects user's input through a form. 
After the form is submitted, the submitted data are validated. If the 
user's input for a certain entry is wrong, there would be a hyperlink 
warning message by clicking on which the user will be sent to form page 
. My current problem is when the user is sent to form page, his / her 
previous inputs are gone. How can I make user's previous inputs show on 
the form? Can any of you give me some hint please?

Blessings,
Rocky