Add items to the Ubercart cart with custom forms
The request for more robust Ubercart add to cart forms comes up fairly regularly. People generally have in mind the sort of form that allows customers to specify quantities for a set of products and add them to the cart all at once. The request came up so often that I put a short explanation on how to accomplish this through a custom form into an FAQ post on Ubercart.org.
This article will walk through a very basic example of how you can use the Ubercart function uc_cart_add_item() in a custom form submit handler to add multiple items to the cart at once. This article assumes a basic knowledge of Drupal's Forms API. Code examples are from Drupal 6, but they are mostly applicable to Drupal 5 as well.
Step by step guide to upgrade Ubercart from Drupal 5 to Drupal 6