How to change product options automatically

[artteddy]

Hi,

 

I am using PS 1.4.6.2

 

All of the products we offer are unique, so the "quantity in stock" is equal to one. And I need to show sold products without price in a special "Sold" category.

 

Every time after the purchase I have to off "show price" and "available for order" options and change category. How do I set these options automatically at the end of purchasing process?

I guess it's a few lines like:

 

if ( $product->quantity == 0)... $product->available_for_order = 0

 

but I need help with the correct code and the right place for this code.

 

Can anyone help me here?