链表，递归答案

【问题标题】：linked list, recursion链表，递归
【发布时间】：2017-04-21 06:12:57
【问题描述】：

我正在开发一个使用递归反向打印链接列表的程序。我的递归代码似乎只打印出最后一部电影，然后它就停止了。 “gets”在 Microsoft Visual Studio 中不起作用，所以我使用的是在线编译的 c ide，并且无法访问调试器。预期输出如下。代码也贴在下面。

Enter first movie title:
Titanic

Enter your rating<0-10>:
5

Enter next movie title:
Inception

Enter your rating<0-10>:
8

Here is the movie list:                                                                                                                                         
Movie: Titanic  Rating: 8                                                                                                                                       
Movie: Inception  Rating: 9                                                                                                                                     
Display list from tail to head:                                                                                                                                 
Here is the movie list:                                                                                                                                         
Movie: Inception Rating : 9
Movie: Titanic   Rating : 8

实际输出：

Here is the movie list:                                                                                                                                         
Movie: Titanic  Rating: 8                                                                                                                                       
Movie: Inception  Rating: 9                                                                                                                                     
Display list from tail to head:                                                                                                                                 
Here is the movie list:                                                                                                                                         
Movie: Inception Rating : 9

#include <stdio.h>
#include <stdlib.h>      /* has the malloc prototype      */
#include <string.h>      /* has the strcpy prototype      */
#define TSIZE    45      /* size of array to hold title   */

struct film 
{
    char title[TSIZE];
    int rating;
    struct film* next;    /* points to next struct in list */
    struct film* prev;   
};

int main(void)
{
    struct film *head = NULL, *prev, *current, *temp;
    struct film *tail = NULL;
    char input[TSIZE];

    /* Gather  and store information          */
    puts("Enter first movie title:");
    while (gets(input) != NULL && input[0] != '\0')
    {
        current = (struct film *) malloc(sizeof(struct film));  //request a new film struct
        if (head == NULL)       /* first structure       */
            head = current;
        else                    /* subsequent structures */
            prev->next = current;
        current->next = NULL;
        strcpy(current->title, input);
        puts("Enter your rating <0-10>:");
        scanf("%d", &current->rating);
        while (getchar() != '\n')
            continue;
        puts("Enter next movie title (empty line to stop):");
        prev = current;
        tail = current;
    }
    /* Show list of movies                    */
    if (head == NULL)
        printf("No data entered. ");
    else
        printf("Here is the movie list:\n");
    current = head;
    while (current != NULL)
    {
        printf("Movie: %s  Rating: %d\n",
            current->title, current->rating);
        current = current->next;
    }

    puts("Display list from tail to head:");
    if (tail == NULL)
        puts("No data entered.");
    else
        puts("Here is the movie list: ");
    current = tail;
    while (current != NULL)
    {
        printf("Movie: %s Rating : %d\n", current->title, current->rating);
        current = current->prev;
    }

    /* Program done, so free allocated memory */
    current = head;
    while (current != NULL)
    {
        temp = current->next;  
        free(current);
        current = temp;
    }

    return 0;
}

【问题讨论】：

但正如您所说，您的程序中没有递归。（这需要一个调用自身的函数。）
..你甚至根本不需要递归来解决这个问题。
@MichaelWalz 我如何在没有递归的情况下做到这一点？
拿一张纸和一支铅笔，你会发现。这一点都不难。提示：谷歌是你的朋友。

标签： c recursion linked-list

【解决方案1】：

您没有在此处填写结构中的 current->prev 字段：

    if (head == NULL)       /* first structure       */
    {
        head = current;
        current->prev = NULL;
    }
    else                    /* subsequent structures */
    {
        current->prev = prev;
        prev->next = current;
    }

【讨论】：

感谢@koper89 的帮助。

【解决方案2】：

您没有设置插入节点的数据成员prev。你应该写例如

    if (head == NULL)       /* first structure       */
    {
        head = current;
        current->prev = NULL;
    }
    else                    /* subsequent structures */
    {
        prev->next = current;
        current->prev = tail;
    }

考虑到在这个循环中使用变量prev 是多余的。

另外，函数gets 是不安全的，C 标准不再支持。而是使用函数fgets。

【讨论】：