在C中添加到列表和显示列表功能

Question

我有我创建的链接列表。我制作了AddTostart函数，该函数具有HAS2参数，第一个参数是列表的负责人，第二个参数是要插入节点中的数据。我还有DisplayList，该列表仅显示列表中的内容。

代码：

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

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

struct node* addToStart(struct node* head, int d){
    struct node *new = malloc(sizeof(struct node));
    if(new == NULL){
        printf("out of memory");

    }
    else{
        new->data = d;
        new->next = NULL;
        new->next = head;
        head = new;
        return head;

    }
    return 0;
}
void displayList(struct node* head){
    struct node *ptr = head;
    while(ptr != NULL){
        printf("%d -> ",ptr->data);
        ptr = ptr->next;
    }
}
int main() {

    int data=0;
    struct node *head;
    head = malloc(sizeof(struct node));
    if(head == NULL){
        printf("Out of memory");
    }
    head->next = NULL;
    while(data != -1){
        printf("Enter a number to be added to the beginning of the list, -1 to exit.");
        scanf("%d",&data);
        if(data == -1)
            break;
        head = addToStart(head,data);


    }
    printf("Number have been recorded in the list. Here are the numbers");
    displayList(head);
    return 0;
}

列表被显示，但随后我看到了其他奇怪的数字。 IE 40274093。它的问题是什么。

Answer 1

您忘了初始化head-＆gt; data。
不过，您可以将其设置为null，而不是初始化它，然后立即开始调用addtostart。如果将null作为head参数传递到addtostart，则应将Next设置为null并按预期工作。以下内容应解决您的问题：

int main() {

    int data=0;
    struct node *head;
    head = NULL; //Just don't allocate memory for `head` and let the function do it for you
    while(data != -1){
        printf("Enter a number to be added to the beginning of the list, -1 to exit.");
        scanf("%d",&data);
        if(data == -1)
            break;
        head = addToStart(head,data);


    }
    printf("Number have been recorded in the list. Here are the numbers");
    displayList(head);
    return 0;
}

Answer 2

清理一些内联评论：

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

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

struct node* addToStart(struct node* head, int d){
    struct node *new = malloc(sizeof(struct node));
    if(new == NULL){
        printf("out of memory");
    }
    else{
        new->data = d;
//        new->next = NULL; // unnecessary, overwritten in next line
        new->next = head;
//        head = new; // does not change head, better
        return new; // return new instead of head;

    }
    return NULL; // 0; want to return a pointer
}
void displayList(struct node* head){
    struct node *ptr = head; // you could just use head as it is a call-be-value parameter
    while(ptr != NULL){
        printf("%d",ptr->data); // removed "->" here
        ptr = ptr->next;
        if (ptr != NULL) { // want " -> " between elements only
            printf(" -> ");
        }
    }
    printf("\n"); // end output with a newline, see https://stackoverflow.com/questions/27238564/getting-a-weird-percent-sign-in-printf-output-in-terminal-with-c
}
int main() {

    int data=0;
    struct node *head;
/*  
    // the following lines add nothing to the list implementation
    // it is just that all lists now end with a node containing 0 as value.  
    head = malloc(sizeof(struct node));
    if(head == NULL){
        printf("Out of memory");
    }
    head->next = NULL;
*/
    head = NULL; // initialize head to indicate list end
    while(data != -1){
        printf("Enter a number to be added to the beginning of the list, -1 to exit: ");
        scanf("%d",&data);
        if(data == -1)
            break;
        head = addToStart(head,data);
    }
    printf("Numbers have been recorded in the list. Here are the numbers: \n");
    displayList(head);
    return 0;
}

$ gcc -Wall list.c
$ ./a.out         
Enter a number to be added to the beginning of the list, -1 to exit: 1
Enter a number to be added to the beginning of the list, -1 to exit: 2
Enter a number to be added to the beginning of the list, -1 to exit: 3
Enter a number to be added to the beginning of the list, -1 to exit: -1
Numbers have been recorded in the list. Here are the numbers: 
3 -> 2 -> 1
$