if current-next == NULL current-next-next == NULL printf无效的选项请重新输入。n; return;

This code checks if the current node's next node is either NULL or the next node's next node is NULL. If either of these conditions is true, it means that there are not enough nodes in the linked list to perform the desired operation. In this case, the code prints "无效的选项，请重新输入。" (which translates to "Invalid option, please re-enter.") and returns, indicating that the operation cannot be performed.