i can't seem to understand the logic behind linked lists :|

This is a discussion on i can't seem to understand the logic behind linked lists :| within the C Programming forums, part of the General Programming Boards category; and here i've shortended to code even more, i guess it's easier to understand: Code: for (prev=NULL; loc != NULL; ...

  1. #16
    Learner Axel's Avatar
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    and here i've shortended to code even more, i guess it's easier to understand:

    Code:
      	for (prev=NULL; loc != NULL; loc = loc->next)
          	{
    			prev = loc;
          	}
          	
        	prev->next = temp;

  2. #17
    Registered User ssharish2005's Avatar
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    Quote Originally Posted by Axel
    and here i've shortended to code even more, i guess it's easier to understand:

    Code:
      	for (prev=NULL; loc != NULL; loc = loc->next)
          	{
    			prev = loc;
          	}
          	
        	prev->next = temp;
    check for loc->next is not equal to null

    ssharish2005

  3. #18
    Learner Axel's Avatar
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    wouldn'tt that already be handled when i malloc the new node?

  4. #19
    Registered User ssharish2005's Avatar
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    noo. the reason why i said, when u interate through each node u will check for the last node.The way u can find is that the last node next should be null. So when u check for loc->next is equal to null u will come to know that u reached end of the node. and then u can follow with appending a new node.

    ssharish2005
    Last edited by ssharish2005; 10-14-2006 at 04:26 AM.

  5. #20
    The C eater *munch*
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    Quote Originally Posted by Axel
    and here i've shortended to code even more, i guess it's easier to understand:

    Code:
      	for (prev=NULL; loc != NULL; loc = loc->next)
          	{
    			prev = loc;
          	}
          	
        	prev->next = temp;
    this is not quite rite ...

    say u have
    Code:
    "Panda" -> NULL
    on the first iteration, loc = *start yes?
    and then you assign prev to loc...
    Code:
    prev = loc;
    and after that, the for loop checks the nullity of loc
    Code:
    for (prev=NULL; loc != NULL; loc = loc->next)
    .. in this case, no... and then loc goes to the next element which is null...
    Code:
    for(..., loc = loc->next)
    which is a problem because after that
    Code:
    prev = loc; // prev becomes null (but we don't want it to be)
    remember in linked list, the last element isn't denoted by NULL... it's denoted by the last item BEFORE NULL
    NULL is just like '\0' character in string.

    got me? this is exactly what ss was saying
    Last edited by yxunomei; 10-14-2006 at 04:41 AM.

  6. #21
    Learner Axel's Avatar
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    ok i think i've understood my original code now please correct me if i'm wrong.

    We have the first element, Cat already added so:

    Code:
    if (*start == NULL)
    evaluates to false so we go to the else bit.

    Code:
    else
       {
          loc = *start; // MAKE loc point to the start of the list.
          prev = NULL;
    
           for (i=0; loc != NULL; i++) //here we just loop till we find an empty position to append to
           {
      
               	prev = loc; // keep track of the previous node by copying what the current node equals to
                    loc = loc->next; // set loc to the next node
            }
    Code:
    once the loop ends it means we have found an empty position i.e.:
    
    [   CAT  ]    [ NULL ]  
    
    prev              loc
    
     so:
    
     prev->next = temp; 
    
    we just insert the new node AFTER prev->next i.e.:
    
    
    [   CAT  ]    [ DOG (new node inserted) ] 
    
    prev      - >  next

  7. #22
    The C eater *munch*
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    i don't see why you need the i in
    Code:
    for (i=0; loc != NULL; i++)
    just do something like
    Code:
    for(loc = *start; loc != NULL; loc = loc -> next)
    this, not only you make it easier to understand, but also make your code shorter because then you can take out the
    Code:
     loc = *start
    at the start of the else bit.

    better yet
    Code:
    for(loc = *start; loc->next != NULL; loc = loc->next) { 
       // do nothing, it's all done in the loop
    }
    
    loc->next = temp;
    Last edited by yxunomei; 10-14-2006 at 04:40 AM.

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