双向链表的从小到大的插入，删除，遍历，清空

#include<stdio.h> #include<stdlib.h> struct linknode { int data; struct linknode* next; struct linknode* pre; }; struct list { struct linknode* head; struct linknode* tail; }; //结点分配内存 struct linknode* creat_node(int data) { struct linknode* newnode = malloc(sizeof(struct linknode)); if (newnode == NULL) { return; } newnode->data = data; newnode->next = NULL; newnode->pre = NULL; return newnode; } //初始化链表 void init_list(struct list* list) { list->head = creat_node(0); list->tail = creat_node(0); list->head->next = list->tail; list->tail->next = NULL; } //遍历并输出链表中的各个元素 void list_travel(struct list* list) { for (struct linknode* pnode = list->head; pnode != list->tail; pnode = pnode->next) { struct linknode* first = pnode; struct linknode* mid = first->next; struct linknode* last = mid->next; if (empty_list(list)) { printf("链表为空\n"); break; } if (mid != list->tail) { printf("元素为:%d\n", mid->data); } } } //往链表中插入结点 void insert_list(struct list* list, int data) { struct linknode* newnode = creat_node(data); for (struct linknode* pnode = list->head; pnode != list->tail; pnode = pnode->next) { struct linknode* first = pnode; struct linknode* mid = first->next; struct linknode* last = mid->next; if (mid->data >= newnode->data || mid == list->tail) { pnode->next = newnode; newnode->next = mid; mid->pre = newnode; newnode->pre = pnode; break; } } } //从链表中删除节点 void delete_list(struct list* list, int data) { for (struct linknode* pnode = list->head; pnode != list->tail; pnode = pnode->next) { struct linknode* first = pnode; struct linknode* mid = first->next; struct linknode* last = mid->next; if (data == mid->data && mid != list->tail) { first->next = last; last->pre = first; free(mid); break; } } } //清空链表 void clear_list(struct list* list) { while (!empty_list(list)) { struct linknode* first = list->head; struct linknode* mid = first->next; struct linknode* last = mid->next; first->next = last; last->pre = first; free(mid); } } //判断是否为空链表 int empty_list(struct list* list) { if (list->head->next ==list->tail) return 1; return 0; } int main() { struct list list; init_list(&list); for (int i = 10; i < 50; i += 10) { insert_list(&list, i); } list_travel(&list); delete_list(&list, 20); delete_list(&list, 40); list_travel(&list); clear_list(&list); list_travel(&list); return 0; }