why this linked list code in c malfunction? - c

Question

I have written this code in c to implement linked list. while the semantic and syntax are fine, it does not work as it should. For example, when I insert 1 into the list and then print the linked list, it shows that the list is empty.
#include<stdio.h>
#include<stdlib.h>
struct node {
int info;
struct node *next;
}; typedef struct node Node;
void addNode(Node *head, int x)
{
Node *temp;
temp=malloc(sizeof(temp));
temp->info=x;
if (head==NULL)//if this is the first node in the list
{
head=temp;
temp->next=NULL;
}
else //if not, add it as the head
{
temp->next=head;
head=temp;
}
}
void appendNode(Node *head, int x)
{
Node *rear =head;
Node *temp= malloc(sizeof(temp));
temp->info=x;
temp->next=NULL;
while (rear->next!=NULL)
rear=rear->next;
rear->next=temp;
rear=temp;
}
void insertNodeafter(Node *head, int location, int x)
{
int i;
Node *before, *after = head;
Node *temp= malloc(sizeof(temp));
temp->info=x;
for (i=0;i<location;i++)
before=before->next;
after=before->next;
temp->next=after;
before->next=temp;
}
void insert(Node *head, int x)
{
int c=0;
Node *temp;
temp=head;
if(temp==NULL)
{
addNode(temp,x);
}
else
{
while(temp!=NULL)
{
if(temp->info<x)
c++;
temp=temp->next;
}
if(c==0)
addNode(temp,x);
else if(c<listSize())
insertNodeafter(temp,x,++c);
else
appendNode(temp,x);
}
}
int listSize()
{
Node *head, *n;
int c=0;
n=head;
while(n!=NULL)
{
n=n->next;
c++;
}
return c;
}
void DisplayLinkedList(Node* head)
{
Node *rear=NULL;
if (head==NULL)
printf("list is empty!\n");
else
{
rear=head;
while (rear!=NULL)
printf("%d |---> ", rear->info);
rear=rear->next;
}
}
int getNextNode(Node *head)
{
if (head == NULL)
return -1;
else
return head->next->info;
}
Node* deleteNode(Node *head, int x)
{
Node *temp;
if (head == NULL)
return NULL;
else
{
if (head->info==x)
{
temp = head->next;
free(head);
head=temp;
return head;
}
else
{
deleteNode(head->next,x);
return head;
}
}
}
void main()
{
int i=0;
Node *myNode;
insert(myNode,1);
DisplayLinkedList(myNode);
}

Answer 1

Because you are using Node* variable instead of using Node** variable in function parameter. Since you are using Node* so changes done in variable head is local to that function. If you want to reflect these changes even after function call(which you obviously wants to) then use Node** and use it accordingly in your code.

Answer 2

As the previous poster has mentioned, it is best to use Node** variable to reflect changes after a function call. If you wanted to use Node*, you'd have to return Node* back to main to print from it.
I pared your code down to add the 1, using AddNode, insert and DisplayLinkedList and it is now displaying correctly with the code below.
You should also set Node* to NULL in main to initialize the empty linked list. Check your DisplayLinkedList function - you're missing curly brackets in the while loop. It was only reading the printf line and not traversing the list, leading to an infinite loop.
Best practice is to debug and test as you are creating this program.
#include<stdio.h>
#include<stdlib.h>
#include "stack.h"
void main()
{
int i=0;
Node *myNode;
myNode = NULL;
insert(&myNode,1);
DisplayLinkedList(myNode);
}
void addNode(Node **head, int x)
{
Node *temp;
temp=malloc(sizeof(temp));
temp->info=x;
if (*head==NULL)//if this is the first node in the list
{
*head=temp;
temp->next = NULL;
}
else //if not, add it as the head
{
temp->next=*head;
*head=temp;
}
}
void insert(Node **head, int x)
{
int c=0;
Node *temp;
temp=*head;
if(temp==NULL)
{
addNode(head ,x);
}
}
void DisplayLinkedList(Node* head)
{
Node *rear=NULL;
if (head==NULL)
printf("list is empty!\n");
else
{
rear=head;
while (rear!=NULL)
{
printf("%d |---> ", rear->info);
rear=rear->next;
}
}
}