链表的创建，插入，逆置，输出，取中间节点，输出，释放

初学链表，相互交流

#include <stdio.h>
#include <stdlib.h>
 
typedef struct data data;
struct data
{
    int value;
    data* pnext;
    data* plast;
};
 
data* create(int n);
void insert(data* head);
void reverse(data* head);
void print(data*head);
int mid(data* head);
void pfree(data* head);
 
 
int main(void)
{
    int n=5;
    data* head=NULL;
    head=create(n);
    insert(head);
    reverse(head);
    int zhong=mid(head);
    printf("mid_value=%d\n",zhong);
    print(head);
    pfree(head);
    return 0;
}
 
data* create(int n)
{
    data *head=NULL,*p=NULL,*l=NULL;
    for(int i=0;i<=n;i++)
    {
        if(i==0){
            p=(data*)malloc(sizeof(data));
            head=p;
            head->plast=NULL;
        }
        else{
            p=(data*)malloc(sizeof(data));
            l->pnext=p;
            p->plast=l;
            printf("输入第%d个数:",i);
            scanf("%d",&p->value);
        }
        l=p;
        p->pnext=NULL;
    }
    return head;
}
 
 
void insert(data* head)
{
    int new_value;
    printf("Input the new_value:");
    scanf("%d",&new_value);
    data *pcurrent=NULL,*p=NULL,*temp=NULL;
    pcurrent=head->pnext;
    p=(data*)malloc(sizeof(data));
    p->value=new_value;
    if(new_value<head->pnext->value)//小于第一个节点
    {
        temp=head->pnext;
        head->pnext=p;
        p->pnext=temp;
        return;
    }
    while(pcurrent!=NULL&&pcurrent->value<new_value)
    {
        temp=pcurrent;
        pcurrent=pcurrent->pnext;
    }
    if(pcurrent!=NULL){//在中间插入
        p->pnext=pcurrent;
        pcurrent->plast=p;
    }
    else{//在结尾插入
        p->pnext=NULL;
    }
    //必执行的代码
    temp->pnext=p;
    p->plast=temp;
}
 
 
void reverse(data*head)
{
    data *temp=NULL,*p=NULL;
    temp=head->pnext;
    head->pnext=NULL;
    while(temp)
    {
        p=temp;
        temp=temp->pnext;
        p->pnext=head->pnext;
        head->pnext=p;
    }
}
 
 
int mid(data*head)
{
    data *pmid=head,*pl=head;
    while(pl&&pl->pnext)
    {
        pmid=pmid->pnext;
        pl=pl->pnext->pnext;
    }
    return pmid->value;
}
void print(data* head)
{
    data* p=head->pnext;
    while(p)
    {
        printf("\t%d",p->value);
        p=p->pnext;
    }
}
 
 
void pfree(data* head)
{
    data* p=NULL;
    while(head)
    {
        p=head;
        head=head->pnext;
        free(p);
    }
}