DaniWeb Forum Index > Software Development > C

C RSS

pls help. link list prob

Please support our C advertiser: Programming Forums - DaniWeb Sister Site

•

Join Date: Sep 2008

Posts: 1

Reputation: aoi is an unknown quantity at this point

Solved Threads: 0

aoi

Offline

Newbie Poster

pls help. link list prob

Sep 27th, 2008

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
t=malloc(sizeof(NODE));
		t->lname[i]=ln[i];
		t->fname[i]=fn[i];
		t->add[i]=ad[i];
		t->telno[i]=tn[i];
		t->next=NULL;
 
		i++;
 
 
	if(*h==NULL){
 
		printf("\nCreating record...");
		*h=t;
 
	}
	else{
		p=*h;
 
		if(p->next!=NULL)
		{
			while(p->next!=NULL){
				if(strcmp(p->lname[i],ln[i])>=0){
					p->prev->next=t;
					t->next=p;
				}
				p->prev=p;
			}
		}
		else
		{
			if(strcmp(p->lname[i],ln[i])>=0)
			{
				p->next=t;
				t->prev=p;
				t->next=NULL;
			}
			else
			{
				p->prev=t;
				t->next=p;
			}
			*h=p;
		}
	}
t=malloc(sizeof(NODE));
		t->lname[i]=ln[i];
		t->fname[i]=fn[i];
		t->add[i]=ad[i];
		t->telno[i]=tn[i];
		t->next=NULL;

		i++;


	if(*h==NULL){

		printf("\nCreating record...");
		*h=t;

	}
	else{
		p=*h;

		if(p->next!=NULL)
		{
			while(p->next!=NULL){
				if(strcmp(p->lname[i],ln[i])>=0){
					p->prev->next=t;
					t->next=p;
				}
				p->prev=p;
			}
		}
		else
		{
			if(strcmp(p->lname[i],ln[i])>=0)
			{
				p->next=t;
				t->prev=p;
				t->next=NULL;
			}
			else
			{
				p->prev=t;
				t->next=p;
			}
			*h=p;
		}
	}

could help me with my code? i can't make the 3rd node and when i try to make the 2nd node and print it the 2nd node will replace the data inside my first node.

Last edited by aoi; Sep 27th, 2008 at 11:04 am.

•

Join Date: Apr 2008

Posts: 671

Reputation: Freaky_Chris is a jewel in the rough

Solved Threads: 113

Freaky_Chris Freaky_Chris is offline

Offline

Practically a Master Poster

Re: pls help. link list prob

Sep 27th, 2008

Hmm lets try adding code tags, so it becomes a bit more readable. Also couldyou give us a little clue as to what problems you are actually having cause thats alot to look over when we don't know what were looking for

Chris

•

Join Date: Sep 2008

Posts: 273

Reputation: Sci@phy will become famous soon enough

Solved Threads: 42

Sci@phy

Offline

Posting Whiz in Training

Re: pls help. link list prob

Sep 27th, 2008

I presume h is a pointer to the first node? Like:
NODE* h;

In that case, this code:

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
if(*h==NULL)
//should be:
if (h == NULL)
if(*h==NULL)
//should be:
if (h == NULL)

Because (*h) is actualy the node itself, and not a pointer.

•

Join Date: Jul 2008

Posts: 113

Reputation: ahamed101 is an unknown quantity at this point

Solved Threads: 14

ahamed101

Offline

Junior Poster

Re: pls help. link list prob

Sep 28th, 2008

Hi there,

Please try to be more specific about your queries... Looks like this is a doubly linked list... a queue?...

Like Sci@phy said, if h is a pointer to first node, you should use

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
if(h == NULL)
if(h == NULL)

or if it is an argument you have passed to this function of type NODE**, then its correct...

Further more, do a type cast while memory allocating, like

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
t=(NODE *)malloc(sizeof(NODE));
t=(NODE *)malloc(sizeof(NODE));

How many nodes are you trying to add at one go?... And are you trying to add the node in a reverse manner?

regards,
Ahamed.

•

Join Date: Dec 2006

Posts: 241

Reputation: ssharish2005 is on a distinguished road

Solved Threads: 20

ssharish2005 ssharish2005 is offline

Offline

Posting Whiz in Training

Re: pls help. link list prob

Sep 28th, 2008

•

t=(NODE *)malloc(sizeof(NODE));

Why the hell would you cast the malloc. You shouldn't do that! Read this.

@OP for me most of of the things seems to be fine, except the head node pointer deferenceing like it has been mentioned by others already. Unless you've got your head node like this

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
void Insert( NODE **h, data );
void Insert( NODE **h, data );

???

ssharish

Last edited by ssharish2005; Sep 28th, 2008 at 8:15 pm.

"Any fool can know, point is to understand"

•

Join Date: Oct 2007

Posts: 305

Reputation: stilllearning has a spectacular aura about

Solved Threads: 43

stilllearning stilllearning is offline

Offline

Posting Whiz

Re: pls help. link list prob

Sep 30th, 2008

I think what you are trying to do is insert values in a doubly linked list in alphabetical order by the last name ?

if so, you aren't going about it correctly .. lets assume you have a set of 5 elements you want to insert in the list; We'll try to insert them in descending order by the last name..

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
 
/* lets insert 5 elements in the list */
  for(j = 0; j < 5; j++){
 
    /* there are no elements in the list. add the first one */
    if(h==NULL){
      h=&t[j];
    }
    else{
      p      = h; 
      done = 0;
      /* lets try to figure out the node, around which we want to 
         insert this new element */ 
      while(p->next != NULL && !done){
        if(strcmp(p->lname,t[j].lname) >= 0){
          p = p->next;
        }
        else{
          done = 1;
        }
      }
      /* do we want to insert the element before the current node
         or after the current node ? */ 
      if(strcmp(p->lname,t[j].lname)>=0){
        /* after -- manipulate the prev and next pointers 
           for the new node. the prev pointer for the
           node after the current node and the next pointer 
           for the current node */ 
        t[j].next       = p->next; 
        t[j].prev       = p;
        if(p->next)
          p->next->prev = &t[j];
        p->next         = &t[j];
      }
      else{
        /* before -- manipulate the prev and next pointers 
           for the new node. the next pointer for the
           node before the current node and the prev pointer 
           for the current node */ 
        t[j].prev       = p->prev;
        t[j].next       = p;
        if(p->prev)
          p->prev->next = &t[j];
        p->prev         = &t[j];         
      }
    }
 
  }
 
/* lets insert 5 elements in the list */
  for(j = 0; j < 5; j++){

    /* there are no elements in the list. add the first one */
    if(h==NULL){
      h=&t[j];
    }
    else{
      p      = h; 
      done = 0;
      /* lets try to figure out the node, around which we want to 
         insert this new element */ 
      while(p->next != NULL && !done){
        if(strcmp(p->lname,t[j].lname) >= 0){
          p = p->next;
        }
        else{
          done = 1;
        }
      }
      /* do we want to insert the element before the current node
         or after the current node ? */ 
      if(strcmp(p->lname,t[j].lname)>=0){
        /* after -- manipulate the prev and next pointers 
           for the new node. the prev pointer for the
           node after the current node and the next pointer 
           for the current node */ 
        t[j].next       = p->next; 
        t[j].prev       = p;
        if(p->next)
          p->next->prev = &t[j];
        p->next         = &t[j];
      }
      else{
        /* before -- manipulate the prev and next pointers 
           for the new node. the next pointer for the
           node before the current node and the prev pointer 
           for the current node */ 
        t[j].prev       = p->prev;
        t[j].next       = p;
        if(p->prev)
          p->prev->next = &t[j];
        p->prev         = &t[j];         
      }
    }

  }

•

Join Date: Jul 2008

Posts: 113

Reputation: ahamed101 is an unknown quantity at this point

Solved Threads: 14

ahamed101

Offline

Junior Poster

Re: pls help. link list prob

Sep 30th, 2008

•

Originally Posted by ssharish2005

Why the hell would you cast the malloc. You shouldn't do that! Read this.

@OP for me most of of the things seems to be fine, except the head node pointer deferenceing like it has been mentioned by others already. Unless you've got your head node like this
Help with Code Tags

c Syntax (Toggle Plain Text)
void Insert( NODE **h, data );
void Insert( NODE **h, data );
???

ssharish

Thanks for that info... i wasn't aware of that...