data attribute from anchor not sending value ti hidden input [closed]

Since you tagged this question with jQuery, I'll give you the jQuery answer. This should work:

$(function(){
    $('a.productin').click(function(){
        $('input:hidden[name="productid"]').val($(this).data('pid'));
    });
});

FYI - It is normal procedure in Stack Overflow to post the code you have tried on your own. We are here to help you fix issues with your code, not to write your code for you. In the future do a search for an answer before you ask the question and give it a shot on your own. Then, you can ask why your code didn't work posting the relevant code for us to see. That's is why your question was voted down.

It is also normal procedure for the downvoter to explain why he voted it down.