update Qty in shopping cart

Hello,
I have Cart.aspx (showing all items which user selected) and I load the quantity and all data from database and inserting the quantity in HTMLinput text like this
<input name='cartID' value='qtyfromdatabase' runat='server' /> and After finishing the loop of loading it will be like this

<input name='1' value='1' runat='server' /> <input name='3' value='2' runat='server' /> <input name='5' value='7' runat='server' /> <input name='10' value='1' runat='server' /> And I added button for updating the quantity but:
1- How can I know the ID of cart?
2- How can I know the Qty value to update?

Regards.