C 链表在末尾添加项目

Question

我正在编写一个在现有链表末尾添加节点的程序。 问题是它似乎没有将硬编码值7 分配给链表最后一个元素的struct node 的变量nr。 代码如下：

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

struct node {
    int nr;
    struct node *next;
};

void addNodes(struct node **head, int n);
void displayList(struct node *head);
void addItemLast(struct node *head);

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

    printf("Introduceti numarul de noduri: ");
    scanf("%d", &n);

    addNodes(&head, n);
    displayList(head);
    addItemLast(head);
    displayList(head);

    return 0;
}

void addNodes(struct node **head, int n) {
    *head = (struct node*)malloc(sizeof(struct node));
    struct node *current = *head;

    printf("\nIntroduceti %d noduri:\n", n);
    for(int i = 0; i < n; i++) {
        printf("Element %d = ", i+1);
        scanf("%d", &(current -> nr));

        current->next = (struct node*)malloc(sizeof(struct node));
        current = current->next;
    }
    current->next = NULL;
}

void displayList(struct node *head) {
    struct node *current = head;
    int i = 1;

    printf("\nElementele introduse sunt:\n");
    while(current->next != NULL) {
        printf("Elementul %d = %d\n", i, current->nr);

        current = current->next;
        i++;
    }
}

void addItemLast(struct node *head) {
    struct node *temp = head, *last;
    last = (struct node*)malloc(sizeof(struct node));

    if(last == NULL) {
        printf("\nMemory cannot be allocated!\n");
    } else {
        last->nr = 7;
        last->next = NULL;

        while(1) {
            if(temp->next == NULL) {
                temp->next = last;
                break;
            }
            temp = temp->next;
        }
    }
}

最后一个函数 addItemLast() 没有按预期工作。

这是输出：

Introduceti numarul de noduri: 3

Introduceti 3 noduri:
Element 1 = 1
Element 2 = 2
Element 3 = 3

Elementele introduse sunt:
Elementul 1 = 1
Elementul 2 = 2
Elementul 3 = 3

有问题的函数运行后，我得到这个输出：

Elementele introduse sunt:
Elementul 1 = 1
Elementul 2 = 2
Elementul 3 = 3
Elementul 4 = 13383248

元素 4 不包含硬编码值 7，而是有一个垃圾值，我不知道为什么。

Answer 1

您对addNodes 的实现不正确，假设我输入n = 2，创建了3 个节点但只调用了两次scanf 函数，因此您在某些节点中有垃圾值（nr 未设置)。

重新实现它（如果addItemLast函数被正确实现，它就可以工作）：

void addNodes(struct node **head, int n){
    printf("\nIntroduceti %d noduri:\n", n);
    for(int i = 0; i < n; i++){
        struct node* last = addItemLast(*head);
        if (*head == NULL)
            *head = last;

        printf("Element %d = ", i);
        scanf("%d", &(last -> nr));
    }
}

---

当您想调用此函数但head 是NULL 时，您需要更改addItemLast 来处理大小写（如果不测试这种情况，您的程序会在调用addItemLast 以获取空列表时崩溃）：

struct node* addItemLast(struct node *head){
    struct node *temp = head, *last;

    last = (struct node*)malloc(sizeof(struct node));
    if (head == NULL)  // <---------
    {
        last->nr = 7;
        last->next = NULL;
        return last;
    }

    if(last == NULL){
        printf("\nMemory cannot be allocated!\n");
    }else{
        last->nr = 7;
        last->next = NULL;

        while(1){
            if(temp->next == NULL){
                temp->next = last;
                break;
            }
            temp = temp->next;
        }
    }
    return last;
}

---

最后显示列表的函数应该是：

   void displayList(struct node *head){
        struct node *current = head;
        int i = 1;

        printf("\nElementele introduse sunt:\n");
        while(current != NULL){  // <---------
            printf("Elementul %d = %d\n", i, current->nr);

            current = current->next;
            i++;
        }
    }

Answer 2

访问current的元素时不必检查是否current->next != NULL。

将你的while循环更改为：

while(current != NULL){
        printf("Elementul %d = %d\n", i, current->nr);

        current = current->next;
        i++;
    }