堆栈清除后打印链表时的Segfault

To be more specific, this code is supposed to be a lesser clone of the Unix function dc. The linked list seems to be working fine. If I attempt to use c to clear the memory, add more numbers, then print again with f I get a segfault. It seems to be printing what should be the Null Node in the linked list. To be more specific, this code is supposed to b