创建一个链表+添加新节点+打印列表，但无法弄清楚为什么它不起作用

Question

所以我正在尝试创建一个链表，它具有在列表的开头添加一个新节点的功能，然后打印出列表。我是一名新手编码员，仍在学习如何执行此操作，当我执行代码时，没有打印任何内容..

#include <stdio.h>

typedef char DATA;
struct node
{
    DATA d;
    struct node *next;
};

int main()
{
    struct node *header = NULL;
    struct node *second = NULL;
    struct node *third = NULL;

    header->d = 'a';
    header->next = second;

    second->d = 'b';
    second->next = third;

    third->d = 'c';
    third->next = NULL;

    struct addnew;

    printList(header);
}

struct node *addnew(node, d, header)
{
    struct node *addnew = header;

    addnew->d = 'k';
    addnew->next = header;

    return addnew;
}

int printList(node, next, header)
{
    struct node *current = header;

    while (next != 'NULL')
    {
        printf('/c', current->d);
        current = current->next;
    }

    return current->d;
}

Answer 1

程序可以如下所示（未经测试）

#include <stdio.h>
#include <stdlib.h>

typedef char Data ;

struct node 
{
    Data d ;
    struct node *next ;
};

struct node * addNew( struct node *head, Data value )
{
    struct node *new_node = malloc( sizeof( struct node ) );

    if ( new_node != NULL )
    {
        new_node->d = value;
        new_node->next = head;
        head = new_node;
    }

    return head;
}

void printList( struct node *head )
{
    for ( ; head; head = head->next ) printf( "%c ", head->d );
}

struct node * freeList( struct node *head )
{
    while ( head != NULL )
    {
        struct node *tmp = head;
        head = head->next;
        free( tmp );
    }

    return head;
}

int main( void )
{
    struct node *head = NULL;

    head = addNew( head, 'a' );
    head = addNew( head, 'b' );
    head = addNew( head, 'c' );

    printList( head );
    printf( "\n" );

    head = freeList( head );
}

至于你的代码，那么它包含很多错误。例如，您没有为列表的元素分配内存。您只定义了指向未分配元素的指针，并将 NULL 分配给这些指针。

struct node *header = NULL;
struct node *second = NULL;
struct node *third = NULL;

接下来的语句

header->d = 'a';
header->next = second;
//..

错了。

还有这个声明

struct addnew;

没有意义。

并且您没有正确定义函数。

Answer 2

@jazuze 很多错误。就算我在学链表，也没关系。我在下面评论了您需要更正的区域。我已经编译了您的代码并进行了更正，并且它可以正常工作，但我不会轻易为您提供解决方案。我建议你在下面工作::

    #include <stdio.h>

typedef char DATA ;     //why do you need to typedef char

struct node {
DATA d ;
struct node * next ;
};

int main (){

struct node* header = NULL;
struct node* second = NULL;
struct node* third = NULL;

header->d = 'a';
header->next = second;

second->d = 'b';
second->next = third;

third->d = 'c';
third->next = NULL;

struct addnew;
printList(header);


}

// place all functions before main

struct node* addnew (node, d, header){  //should be struct node* addnew(struct node* header). This whole function needs to be corrected

struct node* addnew = header;   //incorrect logic. You need to malloc addnew first so that you get a new node in memory
addnew->d = 'k';
addnew->next = header;

return addnew;  //you lose the header

}

int printList(node, next, header){  //(node, next, header) what is this?? It should be printList(struct node* header)
struct node *current = header;

while (next != 'NULL'){     // incorrect logic. What is next. Should be (current != NULL)
    printf('/c', current->d);   //should be printf(“%c”, current->d);
    current = current->next;
}

return current->d;      //why return current->d
}

创建一个链表+添加新节点+打印列表，但无法弄清楚为什么它不起作用

creating a linked list + add new node + print the list and cannot figure out why it's not working

c

pointers

linked-list