/*look at the use of structures and pointers to produce a
 double linked list that lists events in time order*/
#include <stdio.h>
#include <malloc.h>
#include <string.h>


int main (void)
{
  int cont,time;
  typedef struct
  {
      int time;
      struct event *fptr,*bptr; 
  } event;
  
  event *baseptr,*newptr,*tempptr,*tf,*tb;

  /* create the base element for the queue */
  baseptr = (event *) malloc (sizeof (event)); 
  
  /* set up the base of the queue to point to itself with time = 0 */
  baseptr->time = 0;
  baseptr->fptr = baseptr;
  baseptr->bptr = baseptr;
  
  /*enter a loop to collect events */
  time = 999;
  while (time > 0)
  {
     printf("Enter the time for the next event (t = 0 for quit) ");
     scanf("%i",&time);

     if (time == 0) printf("quiting\n"); else
     {
       
       /*create a new pointer */
       newptr = (event *) malloc (sizeof (event));
       newptr->time = time;
       newptr->bptr = newptr; /* initialise */
       newptr->fptr = newptr;
     
       /* place the event into the double linked list in the correct place */
       tempptr = baseptr; /*start off at the root */
       cont = 1;
       do /* loop to work back until correct entry point found */
       {
         tempptr = tempptr->bptr;
         if (newptr->time > tempptr->time) cont = 0; 
         if (tempptr == baseptr) cont = 0;
       } while (cont == 1);

       /* rearrange the pointers to enter the new event */
       newptr->fptr = tempptr->fptr;
       newptr->bptr = tempptr;
       tb = tempptr->fptr;
       tb->bptr = newptr; 
       tempptr->fptr = newptr;
    }
  } /* end of entering new events */
  
  /* now we will write the events out in order */
  tempptr = baseptr->bptr;
  printf("Event pointer %p time = %i\n",tempptr,tempptr->time);
  while (tempptr != baseptr)
  {
      tempptr = tempptr->bptr;
      printf("Event pointer %p time = %i\n",tempptr,tempptr->time); 
  }  
}