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simple example of a linked list in a linked list in C

Hi, i have a small question. Can someone give me an example of a linked list in a linked list? so for example the data are classes of students; the first linked list are classes and in each class is a linked list of students. also how do I add/delete/manipulate linked list in linked list?
thanks!
PS: just a small example would do
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Mytix
Asked:
Mytix
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2 Solutions
 
stefan73Commented:
Hi Mytix,
There's nothing mystical about what you want to do.

Just do a proper wrapping of your list functionality, like:

typedef struct Node_s {
    struct Node_s* next, *prev;
} Node;

typedef struct ListHead_s {
    Node* head,*tail;
} ListHead;

...and define the appropriate functions.
From a more abstract view, each school contains a set of classes and each class contains a set of students.
Make sure you separate the "technical" aspects from the "business flow" aspects, e.g.:

void student_enroll_class(Student* student,Class* the_class) /* Don't name anything "class". That's calling for trouble... */
...as a "business flow" step. Within that, you'd handle the list
stuff.

Just write a routine for all things a student can do with a class. Then write the routines for what a school can do with its classes.

(That's an OO-like approach, but in this case, it's pretty much feasible)





Cheers!

Stefan
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Kent OlsenData Warehouse Architect / DBACommented:
Hi Mytix,

Stefan's correct -- there is no magic here.  (Though the concept may be tough to visualize until you've actually used it.)

Break the problem into the sum of its parts.  You've got a structure that defines a class:


typedef struct
{
  int   ClassNumber;
  int   ClassStartTime;
/*  etc  */
  class_t *Next;
  student_t *StudentList;
} class_t;

and a structure that defines a student:

typedef student
{
  int   StudentNumber;
/*  etc  */
  student_t *Next;
};

Tie it all together with a starting point for the class list:

class_t  *ClassList;

Now when you build the structures, you generate data that (conceptually) looks like this:

Class1  ->  Student1  ->  Student2  ->  Student3 ->  ....
   |
   \/
Class2  ->  Student1  ->  Student4  ->  Student5 ->  ....
   |
   \/
Class3  ->  Student4  ->  Student 6 ->  Student 7 -> ...
   |
   \/
...

Your "primary" linked list is class, and within each class you have a list of students.  The thing to remember is that when you build your functions to manage these lists, you build a set of functions to manage classes and another to manage students.  Within the class functions you reference the student lists only when you need access to student data.  Within the student functions, you should never have to reference the class lists.  (Of course, if/when the student data contains the students "list" of classes, this may change.)


Good Luck,
Kent

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MytixAuthor Commented:
thanks for the replies, but i still am stuck (and recovering from my illness)
how do i actually go through the linked list of linked list and add data to them? and do manipulation to these linked list of linked list.
thanks!
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Kent OlsenData Warehouse Architect / DBACommented:
Hi Mytix,

Still no magic here.  (Though there may be a sorcerer or two at work.  :)  )  Break the problem down to it's components.

Let's add student "Jennifer Smith" to "Biology 101".  (Jennifer is much more interesting than John.)

First we find the pointer to the Biology class.

class_t  *ClassList;
class_t  *CurrentClass;
student_t  *CurrentStudent;

  CurrentClass = FindClass (ClassList, "Biology 101");
  if (CurrentClass == NULL)  /*  Class not found  */
    fprintf (stderr, "Class not defined.\n");
  else
  {
    CurrentStudent = FindStudent (CurrentClass->StudentList, "Jennifer Smith");
    if (CurrentStudent == NULL)
      fprintf (stderr, "%s is not registered in this class\n", "Jennifer Smith");
    else
      /*  Student found in this class  */
  }


Good Luck,
Kent
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MytixAuthor Commented:
thats strange, im still quite perplexed:
are the functions FinClass and FindStudent built-in? or must i make those functions?
im thinking of sorting the classes and students; students first then classes, but still cant get around the basic sorting of linked list, much more linked list of linked lists.
thanks for your help
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Kent OlsenData Warehouse Architect / DBACommented:


You're going to have to build these functions yourself.  The standard C libraries provide you with very few "built in" functions for handling linked lists.

Start easy and build up.

Write your AddClass (), ShowClasses(), and FindClass () functions.  Once you've built the linked list of classes we can move on to building the list of lists.


Kent
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