Date: Sat, 21 Jun 1997 00:40:13 -0500 (CDT)
From: Andrew Deren <aderen AT eecs DOT uic DOT edu>
To: sar AT maties DOT sun DOT ac DOT za
cc: djgpp AT delorie DOT com
Subject: Re: Linked lists (please don't kill me!)
In-Reply-To: <33A3D1BF.6BCC@maties.sun.ac.za>
Message-ID: <Pine.SUN.3.95.970621001422.22827B-100000@ernie.eecs.uic.edu>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk

It's not only in DJGPP but any C compiler that you can use linked lists.
Here is an example program, I did not test it so it might contain some
errors:

#include <stdio.h>
#include <stdlib.h>
#incldue <string.h>

#ifndef TRUE
#define TRUE 1
#endif
#ifndef FALSE 
#defien FALSE 0
#endif

//here is the actual linked list structure
typedef struct LIST {
   char name[14];  //let's say it will hold name
   int age;        //and age of a person
   struct LIST *next;  //this is a pointer to the next node
} LIST;


//this function adds new node to the list. Each node
//contains name and age. You have to pass double pointer because
//you have to modify the pointer to the list if it's null
void AddToList(LIST **list, char *name, int age)
{
   LIST *newNode;   //this is the new node 
   //you have to dynamically allocate memory for the node
   //that's the whole point behind liked lists, nodes can
   //be dynamically created
   newNode = (LIST*)malloc(sizeof(struct LIST));
   strcpy(newNode->name,name); //copy the name
   newNode->age = age;   //and age
  
    if (*list == NULL) {  //if the list has not been creaed yet
       *list = newNode;  //the list points to the created node
       (*list)->next = NULL;  //and the next node is null to mark the end
of the list
   }
   else {  //list was already created
      newNode->next = *list;  //add new node at the beginning of the list
      *list = newNode;   //and the list now points to the new beginning
   }
}

//this function recursively searches for the name in the list
//it returns true or false, and stores age of that person in age
int LookForName(LIST *list, char *name, int *age)
{
   //if you reach null, all the nodes of the list were searched
   //and person was not found
   if (list == NULL) return FALSE;
   else if (strcmp(list->name, name) == 0) { //you found that person
      *age = list->age;  //coyp age
      return TRUE;
   }
   else return LookForName(list->next, name, age); //try next node
}

main()
{
   LIST *list = NULL;  //the actual list
   char name[14];   //temp name
   int choice;    //choice of the user
   int age;   //age
   do {  //do loop
      printf("Enter 1 to add name or 2 to look for name\n");
      printf("or enter 0 to ext\n");
      scanf("%d", &choice); //get the choice
      if (choice == 1) {  //add name
         printf("Enter name: ");
         scanf("%s", name);
         printf("Enter age: ");
         scanf("%d", &age);
         AddToList(list, name, age);  //add name to list
      }
      else if (choice == 2) { //look for name
         printf("Etner name: ");
         scanf("%s", name);
         if (LookForName(name, &age)) { //found person
             printf("Person found in list.\n");
             printf("his age is: %d\n", age);
         }
         else {
            printf("Person not found.\n");
        }
      }
      else if (choice == 0) break;
   } while (choice != 0);
}

this little program keeps asking either to add a person to a list or to
find person in the list. I hope this is helpful. If you have more
questions go ahead and ask, but I would recomend to get a book on advanced
C programming. It doen not have to be for DJGPP, get some ANSI C and that
will work.

Andrew Deren
aderen AT eecs DOT uic DOT edu
http://www.geocities.com/SiliconValley/Vista/1042
Get 3 Games PacHorror, Tetris or Kill The Barney with
full source code.

On Sun, 15 Jun 1997 sar AT maties DOT sun DOT ac DOT za wrote:

> Hi!
> 
> I'm a newbie to DJGPP and C itself. Can anybody provide me with some
> sample code as to how to create, modify and erase linked lists under
> DJGPP? I know it has something to do with pointers but I just can't seem
> to get the syntax and the * in the right places.
> 
> Any help will be appreciated!
> 
> Rylan
>