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From: "Bill" <mst3kfan@earthlink.net>
Subject: Re: Code Confusion.
Date: 1997/11/04
Message-ID: <63p118$4l0@bolivia.earthlink.net>#1/1
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References: <345CD154.1249E04E@eng.ua.edu>
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Organization: EarthLink Network, Inc.
Newsgroups: comp.lang.ada
Date: 1997-11-04T00:00:00+00:00
List-Id: <comp.lang.ada>


 Your code only creates one node, stores a value, then links it to itself
Num_Nodes times. That is why they all have the same integer stored in the
record!
 First, the user input code would work better as a seperate proceedure that
passes the integer you want to store in the record.
The value would be passed to a 2nd proceedure that stores nodes in the
linked list.  Make sure you have the store proceedure handle all 4 possible
cases (ie, Store to an empty list, store to the front of the list, store at
the back of the list, store somewhere in the middle). The algorithm you
write will sort by the integer value going in since, being the only
non-access value in the record, it has to be your key.You could create new
nodes like this: (at the front or to an Empty List)

Head: NEW Node(I, Head);

This is a qualified aggregate.
I used I as the in parameter. Remember that the right side of the assignment
statement is always evaluated first in Ada.
 This could be done with local variables when you are searching where to put
the node in the list. That is , assign the new node(with Next set to NULL)to
a temp variable. Use 2 more to keep track of where you are as you search
through the list.  Something like this: (R is a record: just pretend it is
whatever you are passing in).

 Temp:= NEW Node'(R, NULL);
       Previous:= L.Front;
       Current:= L.Front.Next;
       While Previous /= NULL and then
                     R.Student_ID_Number >= Current.Data.Student_ID_Number
loop
         Previous:= Current;
         Current:= Current.Next;
       end loop;
       -- The nodes before and after the new ID number have been found.
       -- Insert between these.
       Temp.Next:= Current;
       Previous.Next:= Temp;
     end if;

Here Student_ID_Number is the key field in the record being passed in. This
is just one piece of an if elsif constuct that handles all 4 cases.
You could then write a proceedure that summarizes the list to the screen.
 Trying to store & summarize a singly linked-list in a single proceedure can
be done, but I think it would work better with 2. Better still with the
operations for the ADT in the package body & then a user interface/test
program seperate (assuming this is a CS homework assignment).

PS: I would make this ADT private & include  exported user-defined
exceptions  as well.

Supreme wrote in message <345CD154.1249E04E@eng.ua.edu>...
>In the following program I am trying to display the values of linked
>list instead my output is
>80 80 80 80 80 80
>instead of 40 50 60 70 80.
>here it is.
>procedure problem is
>    type LIST_NODE;
>    type NODE_PTR is access LIST_NODE;
>    type LIST_NODE is record
>                NUM : INTEGER;
>                NEXT : NODE_PTR;
>     end record;
>
>HEAD,P  : NODE_PTR;
>N, NUM_NODES : INTEGER;
>begin -- lab10A
>    Put("Please enter the the values of the nodes");
>Get( Num_Nodes);
>Head := new NODE;
>New_Line;
>P := Head;
>    for K in 2..NUN_NODES loop
>Head.Next := P;
>P.ALL.NUM := N;
>P := P.Next;
>end loop;
>    Will this allow teh user to assing 20 30 40 50 etc to the linked
>list?
>in other words
>Head.Next := P Should point the Head.next to the Pointer P and
>then P.ALL.NUM :=N should be set to the value of N  ( entered by the
>user)
>then P := P.Next should allow N to be assigned to the next pointer.
>is this right??
>Peace.
>