5.2 List length

How many items are there in a list? Let us consider the cases:

• Base case: the list is empty. An empty list has no items, return 0.
• Recursive step: the list is non-empty. Return one plus the length of the rest of the list.

It is coded as follows:

Line 3 checks to see if the pointer to the list itself is NULL. This is not strictly required if we can assume that the parameter is at least a valid pointer to a list. If the pointer is not NULL, then the expression returns the right hand side of the : operator.

Line 4 checks to see if the list pointed to by pList is empty or not. If so, the embedded ?: expression returns 0. Otherwise, the right hand side of : is evaluated.

Line 5 evaluates iff the pointer is not NULL, and the list pointed to by the pointer is not empty. At this point, we return the sum of 1 (for the first item in the list) and the length of the rest of the list.