Common Errors

1. Linked List traversal errors in Course member functions:
   • for (Node* curr = student_list.get_head(); curr != nullptr; … ) which means that the contents of sentinel is also checked.
   • for (Node* curr = student_list.get_head(); curr->next != nullptr; … ) which means that the last value is omitted.
   • for (Node* curr = student_list.get_head(); curr != nullptr; … ) { if (curr->next->content == … ) } which will dereference nullptr after the last node.


2. Forgetting to increment/decrement size.


3. Forgetting to update tail in remove() when removing the last node for the singly linked list.


4. Technically correct but redundant code:
   • Traversing the linked list from head until finding the node with the same content as del or prev, instead of using the given nodes directly in the function arguments of remove() and insert().
   • Traversing the linked list to count the number of nodes for get_enrolled() and get_waitlisted() instead of directly using get_size().
   • Maintaining tail in the circular doubly linked list instead of just using sentinel->prev.
   • Not correctly using the sentinel in circular doubly linked list during insert() and remove(); still checking for special cases such as inserting first node and removing last node.


5. Forgetting to make the linked list actually circular and doubly linked for the bonus task. Especially, forgetting to initialize sentinel to circularly and doubly point to itself from the very beginning (sentinel->prev = sentinel->next = sentinel;).