3. Circular Lists

A circular list is one in which the last node is followed by the first node:

Circular lists are usually preferable to non-circular ones, for two reasons:

They provide easy access to both ends of a list: notice that we do not need the first pointer in the header, because we can easily reach the first node with L->last->next
the code for processing a circular list is often simpler than the code for processing a non-circular list - mainly because you don't have to constantly check if the next node is defined - it is always defined.

At the implementation level, however, circularity does create one very tricky case that is a very common source of bugs, and that is singleton lists. When there is only one node in a circular list, it points to itself as the next node. You have to think carefully to handle this correctly.