Final answer:
The logical component being used is a c) decision.
Step-by-step explanation:
The logical component being used in this scenario is c) Decision.
When the user clicks the Checkout button, the shopping cart programming logic checks whether the user is already logged in. Based on the result of this check, a decision is made to either continue with the checkout process if the user is logged in, or prompt the user to sign in if they are not logged in.