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linklst1.c

/************************************************************************ 
 *
 * Purpose: To demonstrate 'linked lists' This program will build a
 *        linked list and place data into it. When the data is exausted
 *        the contents of the list are O/P.
 *
 *        This is a "First in First out" (FIFO) list.
 *
 * Author:  M. J. Leslie
 *
 * Date:    11-May-95
 *
 ************************************************************************/

#include <stdlib.h>           /* malloc                     */

/************************************************************************/

struct x {              /* Declare a structure              */
      char name[20]; 
      int age; 
      struct x *next_rec;
      };

/************************************************************************/

main()
{
  struct x *start_pointer;    /* Define pointers to the structure */
  struct x *next_pointer;

                        /* Create some data to be placed in the
                         * Linked list.                     */
  char *names[]=
  {
    "Martin",
    "John  ",
    "Alex  ",
    ""
  };

  int ages[]={32, 43, 29, 0};

  int count=0;                /* General purpose counter.         */

   /*===================================================================*
    =                                                 =
    =       Build a LINKED LIST and place data into it.                 =
    =                                                 =
    *===================================================================*/
       
                        /* Initalise 'start_pointer' by reserving 
                         * memory and pointing to it        */

  start_pointer=(struct x *) malloc (sizeof (struct x));

                        /* Initalise 'next_pointer' to point
                         * to the same location.            */
  next_pointer=start_pointer;

   /*********************************************************************
    *
    *     start_pointer ---
    *                     |
    *                     |
    *                     V
    *               -----------------
    *              |        |    |   |
    *               -----------------
    *                     A
    *                     |
    *                     |
    *      next_pointer ---
    *
    *********************************************************************/

                        /* Put some data into the reserved 
                         * memory.                    */

  strcpy(next_pointer->name, names[count]);
  next_pointer->age = ages[count];

   /*********************************************************************
    *
    *     start_pointer ---
    *                     |
    *                     |
    *                     V
    *               -----------------
    *              |Martin  | 32 |   |
    *               -----------------
    *                     A
    *                     |
    *                     |
    *      next_pointer ---
    *
    *********************************************************************/


                        /* Loop until all data has been read      */

  while ( ages[++count] != 0 )
  {
                        /* Reserve more memory and point to it    */

    next_pointer->next_rec=(struct x *) malloc (sizeof (struct x));


      /******************************************************************
       *
       *     start_pointer ---
       *                     |
       *                     |
       *                     V
       *                 -----------------
       *              |Martin  | 32 | | |
       *               ---------------|-
       *                     A                |
       *                     |                V
       *                     |                ---------------
       *      next_pointer ---             |               |
       *                          ---------------
       *
       ******************************************************************/

    next_pointer=next_pointer->next_rec;

      /******************************************************************
       *
       *     start_pointer ---
       *                     |
       *                     |
       *                     V
       *                 -----------------
       *              |Martin  | 32 | | |
       *               ---------------|-
       *                                      |
       *                                      V
       *                                      ---------------
       *      next_pointer --------------->|               |
       *                          ---------------
       *
       ******************************************************************/

    strcpy(next_pointer->name, names[count]);
    next_pointer->age = ages[count];

      /******************************************************************
       *
       *     start_pointer ---
       *                     |
       *                     |
       *                     V
       *                 -----------------
       *              |Martin  | 32 | | |
       *               ---------------|-
       *                                      |
       *                                      V
       *                                      ----------------
       *      next_pointer --------------->|John   | 43 |   |
       *                          ----------------
       *
       ******************************************************************/

  }

  next_pointer->next_rec=NULL;

   /*===================================================================*
    =                                                 =
    =       Traverse the linked list and O/P all the data within it.    =
    =                                                 =
    *===================================================================*/


  next_pointer=start_pointer;

   /******************************************************************
    *
    *     start_pointer ---
    *                     |
    *                     |
    *                     V
    *                         -----------------
    *                |Martin  | 32 | | |
    *                 ---------------|-
    *                     A            |
    *                     |          V
    *                     |          ----------------
    *      next_pointer ---             |John   | 43 |   |
    *                            ----------------
    *
    ******************************************************************/

  while (next_pointer != NULL)
  {
    printf("%s   ", next_pointer->name);
    printf("%d \n", next_pointer->age);
    next_pointer=next_pointer->next_rec;

      /******************************************************************
       *
       *     start_pointer ---
       *                     |
       *                     |
       *                     V
       *                 -----------------
       *              |Martin  | 32 | | |
       *               ---------------|-
       *                                      |
       *                                      V
       *                                      ----------------
       *      next_pointer --------------->|John   | 43 |   |
       *                          ----------------
       *
       ******************************************************************/
  }
   
}

/************************************************************************ 
 *
 *    Program results.
 *
 * Martin   32 
 * John     43 
 * Alex     29 
 *
 ************************************************************************/


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