Unexpected output in a linked list

Question

Sometime back I asked a question about linked list and got nice replies...Now I've written a new code using the suggestions but I've run into an error. The code is:

#include<stdio.h>
#include<stdlib.h>
typedef struct node
{
    int data;
    struct node *next;
}node;
node *mknode()
{
    return malloc(sizeof(node));
}
void create(node* h, int num)
{
    int i;
    node *temp=h;
    for(i=0;i<num;i++)
    {
        temp->data=i;
        if(i==(num-1))
            temp->next=NULL;
        else
            temp->next=mknode();
        temp=temp->next;
    }
}
node* add_end(node *h,int num)
{
    node *temp;
    if(h==NULL)
    {
        h=mknode();
        temp=h;
        create(h,num);
    }
    else
    {
        temp=h;
        while(h!=NULL){
            h=h->next;}
        h=mknode();
        create(h,num);
    }
    return temp;
}
void display(node *h)
{
    node *temp=h;
    while(temp!=NULL)
    {
        printf("%d->",temp->data);
        temp=temp->next;
    }
}
int main()
{
    node *head=NULL;
    int num;
    scanf("%d",&num);
    head=add_end(head,num);
    head=add_end(head,num);
    display(head);
    //printf("%d",list_len(head));
    free(head);
    return 0;
}

Now since I've called add_end twice for an input of 3 the output should be 0->1->2->0->1->2-> But instead I'm getting 0->1->2->

I've checked this much that the FOR loop inside create function is running 2n times for an input of n. So the problem is that display function encounters a NULL but I can't figure out where in the code is it happening.

All help appreciated. Thanking in advance -user1614886

Mehrwolf · Accepted Answer · 2012-09-04 13:32:38Z

3

In add_end() you do not link the nodes correctly.

[blah blah]
else
{
    temp=h;
    while(h!=NULL){
        h=h->next;}
    h=mknode();
    create(h,num);
}

You advance h until it is NULL but you should only move until h->next == NULL and append your next list there.

answered Sep 4, 2012 at 13:32

Mehrwolf

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3 Comments

user1614886 Over a year ago

Thanks Mehrwolf for your reply...I did what you asked...but to make the code work correctly I had to change h=mknode(); to h->next=mknode(); and pass h->next in create function instead of h...so ultimately isn't it doing the same thing EDIT:No they are different...figured it out :P

Mehrwolf Over a year ago

@user1614886: That was what I intended. First move until h->next == NULL and then append the new end at h->next. This makes the connection between the end of the old list h and the new list h->next.

user1614886 Over a year ago

@Meherwolf: After few more minutes of thinking everything makes sense now. Thanks again.

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