Removing Node from LinkedList - c

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

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 2

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 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;
}