双向链表，两端指向NULL(JAVA思路的C实现)

#include "stdio.h"
#include "stdlib.h"

typedef struct Node{
    int data;
    struct Node *pre;
    struct Node *next;
}line,*pline;

line * initLine(line *head){
    line *node,*rear;
    int length,pos=1,data;
    printf("请输入链表的长度:>");
    scanf("%d",&length);
    if (length<1) return NULL;

    head = (line *)malloc(sizeof(line));
    if(!head) return NULL;
    head->pre = NULL;
    head->next = NULL;
    rear = head;
    printf("请输入第%d个数据:>",pos++);
    scanf("%d",&(head->data));
    
    for (;pos<=length;)
    {
        printf("请输入第%d个数据:>",pos++);
        node = (line *)malloc(sizeof(line));
        if(!node) return NULL;
        scanf("%d",&(node->data));
        node->pre = rear;
        node->next = rear->next;
        rear->next = node;/*这句之前忘了，要注意*/
        rear = node;
    }
    return head;
}



void printLine(line *head)
{
    line *node;
    node = head;
    printf("打印链表:");
    while(node){
        printf("%d ",node->data);
        node = node->next;
    }
    printf("\n");
}

line * insertLine(line *head, int data, int add){
    line *insNode = (line *)malloc(sizeof(line));
    line *node;
    int i;
    if (!insNode) return -1;
    insNode->data = data;
    if (add == 1){
        insNode->pre = NULL;
        insNode->next = head;
        head = insNode;
    }else{
        node = head;
        for (i=1; i<add-1; ++i){
            node = node->next;
        }
        if (node == NULL) {
            printf("#The insert number is out of the sequence bound!\n\
            #please check out the insert number.\n");
            return head;
        }
        insNode->pre = node;
        insNode->next = node->next;

        if(node->next != NULL)
            node->next->pre = insNode; 
        node->next = insNode;        
    }
    return head;
}

line * deleteLine(line *head, int data){
    line *node;
    node = head;
    for (;node != NULL;){
        if (node->data == data){
            node->pre->next = node->next;
            node->next->pre = node->pre;
            free(node);
            node = NULL;
            printf("=====节点删除完毕=====\n");
            return head;
        }
        node = node->next;
    }
    printf("=====哎呦喂！没有您要删除的节点~内!=====\n");
    return head;
}
int main(){
    line *L = initLine(L);/*这句返回值赋值给自己是关键，java这类无指针语言的思路，要利用返回值*/
    L = insertLine(L,30,7);
    L = insertLine(L,15,2);
    printLine(L);
    L = deleteLine(L,30);
    L = deleteLine(L,15);
    printLine(L);
    return 0;
}

输入：5 1 2 3 4 5

输出结果：

请输入链表的长度:>5
请输入第1个数据:>1
请输入第2个数据:>2
请输入第3个数据:>3
请输入第4个数据:>4
请输入第5个数据:>5
#The insert number is out of the sequence bound!
#please check out the insert number.
打印链表:1 15 2 3 4 5
=====哎呦喂！没有您要删除的节点~内!=====
=====节点删除完毕=====
打印链表:1 2 3 4 5