双链表上机操作

#include <stdio.h>
#include <string.h>
#include <malloc.h>
typedef struct Node
{
    int num;
    struct Node *pre;
    struct Node *next;
}mode;

// head为双向链表表头
// dir为排序方向：0为升序，1为降序
void sort_list(mode *head, int dir)
{

    if(head == NULL) return ;
    mode *now_item= head;
    mode *next_item = NULL;
    int tmp = 0;

    while(now_item->next != NULL)
    {
        next_item = now_item->next;
        while(next_item != NULL && next_item->pre != head && (next_item->pre->num > next_item->num) ^ dir)
        {
            tmp = next_item->num;
            next_item->num = next_item->pre->num;
            next_item->pre->num = tmp;
            next_item = next_item->pre;
        }