I have a webpage which requires filling out details by anonymous user, and in the bottom I have put in the captcha control.
During clicking of the submit button, I do the validation and throw out the error. However , the user has to enter all the form data again if the validation fails because all fields get reset.
Is there a way to prevent form fields from being reset when validation fails while running PHP script?

They're called sticky forms. For a simple text element, you simply echo the checked variable in as the element's value.

ie.
html:

 <input type="text" name="email" value = "<?=$_POST['email']?>">