谁能告诉我为什么在末尾插入新节点后链表显示垃圾值？

Question

我在显示链接列表值时遇到问题。显示功能似乎工作正常......直到我在末尾插入一个新节点。我花了很多时间试图解决这个问题，但似乎没有任何效果。它只是不断显示垃圾值。 我的C源代码：

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

int n=0;

typedef struct Student
{
    char name[50];
    int roll;
    struct Student *next;
} st;

void createList(st *head)
{
    st *p;
    p = head;
    int i = 0;
    char x = ' ';

    printf("Enter number of nodes: ");
    scanf("%d", &n);
    scanf("%c", &x);

    for (i = 1; i <= n; i++)
    {
        printf("Enter name: ");
        gets(head->name);
        printf("Enter roll number: ");
        scanf("%d", &(head->roll));
        scanf("%c", &x);
        
        head->next = (st *)malloc(sizeof(st));

        head = head->next;
    }

    head->next = NULL;
}

void display(st *head)
{
    int i=0;

    while(head->next != NULL)
    {
        printf("\nName\t\t:\t%s",head->name);
        printf("\nRoll no.\t:\t%d", head->roll);
        head = head->next;
    }
}
void insertEnd(st* head)
{
    st *p, *newnode;
    p = head;
    char x = ' ';

    newnode = (st*)malloc(sizeof(st));
    printf("Enter name: ");
    gets(newnode->name);
    printf("Enter roll no.: ");
    scanf("%d", &(newnode->roll));
    scanf("%c", &x);
    newnode->next = NULL;
    
    while (p->next != NULL)
    {
        p = p->next;
    }
    p->next = newnode;
    
}

int main()
{
    st *head;
    head = (st *)malloc(sizeof(st));
    createList(head);

    printf("The data entered:\n");
    display(head);
    
    printf("\nInsert data for newnode at the end:\n");
    insertEnd(head);
    
    printf("The data after insertion:\n");
    display(head);
    return 0;
}

输出：

Enter number of nodes: 3
Enter name: Alpha
Enter roll number: 100
Enter name: Beta
Enter roll number: 200
Enter name: Gamma
Enter roll number: 300
The data entered:

Name            :       Alpha
Roll no.        :       100
Name            :       Beta
Roll no.        :       200
Name            :       Gamma
Roll no.        :       300
Insert data for newnode at the end:
Enter name: Delta
Enter roll no.: 400
The data after insertion:

Name            :       Alpha
Roll no.        :       100
Name            :       Beta
Roll no.        :       200
Name            :       Gamma
Roll no.        :       300
Name            :       peÅf╡☺
Roll no.        :       1986622020

正如您在代码输出中看到的，链表显示工作正常，直到我在末尾添加新节点。我看了几个教程，我没有发现我的代码有任何问题。请帮助我找到问题，我是链表新手。

Answer 1

在看到“kaylum”的上述评论之前，我正在测试对代码的调整，但这基本上解决了问题。以下是您的代码的修订版，它恰好实现了 kaylum 评论中列出的想法。

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

int n=0;

typedef struct Student
{
    char name[50];
    int roll;
    struct Student *next;
} st;

void createList(st *head)
{
    st *p;
    p = head;
    int i = 0;
    char x = ' ';

    printf("Enter number of nodes: ");
    scanf("%d", &n);
    scanf("%c", &x);

    for (i = 1; i <= n; i++)
    {
        printf("Enter name: ");
        gets(head->name);
        printf("Enter roll number: ");
        scanf("%d", &(head->roll));
        scanf("%c", &x);

        if (i == n)                     /* Condition the update of the next node along with allocating more memory */
        {
            head->next = NULL;
        }
        else
        {
            head->next = (st *)malloc(sizeof(st));
            head = head->next;
        }                               /* End of the tweaks */
    }

    head->next = NULL;
}

void display(st *head)
{
    int i=0;

    while(head != NULL)     /* This provides a complete list and reacts to the other revision made to the program */
    {
        printf("\nName\t\t:\t%s",head->name);
        printf("\nRoll no.\t:\t%d", head->roll);
        printf("Pointer: %p\n", head);
        printf("Next node: %p\n", head->next);
        head = head->next;
    }
}
void insertEnd(st* head)
{
    st *p, *newnode;
    p = head;
    char x = ' ';

    newnode = (st*)malloc(sizeof(st));
    printf("Enter name: ");
    gets(newnode->name);
    printf("Enter roll no.: ");
    scanf("%d", &(newnode->roll));
    scanf("%c", &x);
    newnode->next = NULL;

    while (p->next != NULL)
    {
        p = p->next;
    }
    p->next = newnode;

}

int main()
{
    st *head;
    head = (st *)malloc(sizeof(st));
    createList(head);

    printf("The data entered:\n");
    display(head);

    printf("\nInsert data for newnode at the end:\n");
    insertEnd(head);

    printf("The data after insertion:\n");
    display(head);
    printf("\n");
    return 0;
}

添加“if”块来调节“malloc”请求，消除了悬空内存分配并正确设置“下一个”指针值。另外，我调整了显示函数中的“while”测试，以配合创建函数中的调整。