为什么我的链表修改在这个 c 代码中不起作用？

Question

这是我的代码，我正在尝试使用带有用户输入的菜单添加、打印、删除、清空列表，但它不保存或输出任何值。我通过调用循环外的函数对其进行了调试，它们可以工作，但问题是调用不会在循环内输出任何内容。

#include <stdio.h>
#include <stdlib.h>
struct node
{
    int data;
    struct node *next;
};

int Length(struct node* head);
void PrintList(struct node* head);
void Add(struct node** headRef, int new );
int Delete(struct node** headRef);
void ZeroList(struct node** headRef);

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

    char enter;
    int x;
    Add( &head, 13 );
    printf("\na(add){x}\nd(del)\nl(ength)\np(rint)\nz(ero)\ne(xit)");
    do
    {
        fscanf(stdin, "%c", &enter);
        struct node *head = NULL;
        switch (enter)
        {
            case 'a': 
                printf("Enter a node: ");
                fscanf(stdin,"%d", &x);
                            Add(&head, x);
                break;
            case 'd':
                printf("Delete\n"); 
                Delete(&head);
                break;
            case 'l': 
                printf("Length");
                Length(head);
                break;
            case 'p':
                printf("printList");
                PrintList(head);
                break;
            case 'z': 
                printf("ZeroList");
                ZeroList(&head);
                break;
        }
    }while (enter != 'e');
    Add(&head, 23);
    PrintList(head);
    return 0;
}



//Debug
 /* Add( &head, 3 );
  Add( &head, 20 );
  Add( &head, 55 );
  Delete(&head);  
    Length(head);
  PrintList(head);
  ZeroList(&head);
   PrintList(head);*/

int Length(struct node* head) {
    struct node *current = head;
    int count = 0;
    while (current != NULL)
    {
        count++;
        current = current->next;
    }
    printf(" Size of head is %d\n", count);
    return(count);
}
void PrintList(struct node* head) {
    struct node *current = head;
    while (current != NULL)
    {
        printf("printing %d\n",  current->data);
        current = current->next;
    }
}
void Add(struct node** headRef, int new) {
    struct node *k = malloc(sizeof(struct node));
    k->data = new;
    k->next = *headRef;
    *headRef = k;
    return;
}
int Delete(struct node** headRef) {
    struct node* current = *headRef;
    if (current == NULL)
    {
        printf("List is empty!\n");
    }
    else
    {
        printf("Deleted value is: %d\n", current->data);
        *headRef = current->next;
        free(current);
    }
    return 0;
}

void ZeroList(struct node** headRef){
    struct node* current = *headRef;
    while (current != NULL)
    {
        current = current->next;
        free(current);
    }
}

Answer 1

循环中的这一点：

case 'a': 
printf("Enter a node: ");
fscanf(stdin,"%d", &x);

你必须添加Add-function:

Add(&head, x);

这不能在循环内，删除它：

struct node *head = NULL;

ZeroList 中还有两个错误。您永远不会释放第一个元素，并且在列表末尾释放 NULL。你可以试试这个：

void ZeroList(struct node** headRef){
    struct node* current = *headRef;
    while (current != NULL)
    {
            struct node* tmp = current;
            current = current->next;
            free(tmp);
    }
    *headRef=NULL;
}

这是我对你的程序的试运行：

a(add){x}
d(del)
l(ength)
p(rint)
z(ero)
e(xit)a
Enter a node: 1
a
Enter a node: 2
a
Enter a node: 3
p
printListprinting 3
printing 2
printing 1