从LinkedList删除节点

Question

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
typedef struct _listnode
{
    int item;
    struct _listnode *next;
} ListNode;

int removeNode(ListNode **ptrHead, int index);
void printList(ListNode *head);
ListNode * findNode(ListNode *head, int index);

int main()
{
    ListNode *head = NULL, *temp=NULL;
    int i = 0;
    int index = 0;
    while (1)
    {
        printf("Enter a integer: ");
        scanf("%d", &i);
        if (i == -1)
            break;
        if (head == NULL)
        {
            head = malloc(sizeof(ListNode));
            temp = head;
        }
        else{
            temp->next = malloc(sizeof(ListNode));
            temp = temp->next;
        }
        temp->item = i;
    }
    removeNode(&head, index);
    return 0;
}

void printList(ListNode *head)
{
    int i = 0;
    if (head == NULL)
        return;
    while (head != NULL)
    {
        printf("%d ", head->item);
        head = head->next;
    }
    printf("\n");
}
ListNode * findNode(ListNode *head, int index)
{
        if (head == NULL || index   <   0)
        return  NULL;

        while (index    >   0){
            head = head->next;
            if (head == NULL)
                return  NULL;
            index--;
        }
        return  head;
}

int removeNode(ListNode **ptrHead, int index)
{
    ListNode *pre, *cur,*temp;
    if (index >= 0)
    {
        printf("Enter index to remove: ");
        scanf("%d", &index);
        if ((pre = findNode(*ptrHead, index - 1)) != NULL)
        {
            cur = pre->next;
            temp = cur;
            pre->next = cur->next;
            free(temp);
            printList(*ptrHead);
        }

    }
    return -1;
}

I successfully revamp my code and now I am able to remove the node and display out, but the whole program just crash after my printList function. It does not go back to remove node and I cant continue removing other indexes.

Output:
Enter a value: 2 
Enter a value: 4 
Enter a value: 6 
Enter a value: 8 
Enter a value: -1 
Enter index to remove: 2 
Current list: 2 4 8 
Enter index to remove: 0 
Current list: 4 8 
Enter index to remove: -1

Answer 1

removeNode(head, index); should be removeNode(&head, index);

And printList(ptrHead); should be printList(*ptrHead); (in removeNode ) I have the feeling this piece of code goes crazy that's why your app is not responding anymore.

What compiler do you use? It should have warned you.

Answer 2

when you enter index = 0, the inner if block of removenode function will not be executed as the findnode functin returns NULL. But in your output for index = 0 you got node 2 removed. How did u get that?

Answer 3

In your updated code:

• You still do not set next to NULL.
• You never increment index when you fill list.
• You do not check if scanf() succeeds.

• There is no need to use pointer to pointer in removeNode() , you can use:

   int removeNode(ListNode *ptrHead, int index); 

• You have added removeNode() in printList() which is really out of place.
• You do not have any free function for the list.
• ...

---

Original answer to original code:

---

• Missing header file.
• Miss match between function signatures in declaration and definition.
• You never set next to NULL.
• You do not free list before exit.
• ...

Code with some comments:

/* MISSING: <stdio.h> */
#include <stdlib.h>
typedef struct _listnode
{
    int item;
    struct _listnode *next;
} ListNode;

/* Signature miss-match */
int removeNode(ListNode **ptrHead, int index);
void printList(ListNode *head);
ListNode *findNode(ListNode *head, int index);

int main()
{
    ListNode *head = NULL, *temp=NULL;
    int i = 0;
    int index = 0;
    while (i != -1)
    {
        printf("Enter a integer: ");
        scanf("%d", &i);
        /* If -1 entered, -1 will be added to list. */
        if (head == NULL)
        {
            head = malloc(sizeof(ListNode));
            temp = head;
        }
        else{
            temp->next = malloc(sizeof(ListNode));
            temp = temp->next;
        }
        temp->item = i;
        /* temp->next never set to NULL */
    }
    /* Miss match between function signature and call. */
    removeNode(head, index);

    /* No freeing of list before exit. */
    return 0;
}

void printList(ListNode *head)
{
    /* Redundant check of head != NULL */
    if (head == NULL)
        return;
    while (head != NULL)
    {
        printf("%d", head->item);
        head = head->next;
    }
}
ListNode *findNode(ListNode *head, int index)
{
        if (head == NULL || index   <   0)
        return  NULL;

        while (index    >   0){
            head = head->next;
            if (head == NULL)
                return  NULL;
            index--;
        }
        return  head;
}

/* Why pass index as argument when it is not used? */
int removeNode(ListNode **ptrHead, int index)
{
    ListNode *pre, *cur,*temp;
    printf("Enter index to remove: ");
    scanf("%d", &index);
    /* Here you should check < 0, not  != -1. 
       What if user enters -9999 ? */
    if (index != -1)
    {
        if ((pre = findNode(*ptrHead, index - 1)) != NULL)
        {
            cur = pre->next;
            temp = cur;
            pre->next = cur->next;
            free(temp);
            /* Bad return statement, should be int */
            return;
        }
        /* You only print list if none was removed. */
        /* Miss match between function signature and call. */
        printList(ptrHead);
    }
    return -1;
}