L-28 MCS 275 Wed 21 Mar 2001

/* L-28 MCS 275 Wed 21 Mar 2001 insertion and deletion */

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

typedef struct list LIST;

struct list
{
   int  head;
   LIST *tail;
};

void print ( LIST *l );
/* prints the elements in a list */

LIST *create ( int n );
/* returns a list that contains n */

LIST *insert ( LIST *current, LIST *next, int n );
/* inserts the number n in between current and next,
   returns the new value for next */

LIST *delete ( LIST *current, LIST *next );
/* deletes the element where next is pointing to, 
   returns the new value for next */

void destroy ( LIST *l);
/* destroys the list, freeing the allocated memory */

int main()
{
   LIST *l,*current,*next;
   int n,ind;

   printf("Creating list of positive numbers...\n");
   l = NULL;
   for (;;)
   {
      printf("  Give a positive number (0 to stop) : ");
      scanf("%d", &n);
      if (n <= 0)    
         break;
      else
      {
         if (l == NULL)
            l = create(n);
         else if (l->tail == NULL)
         {
            l->tail = create(n);
            current = l;
            next = l->tail;
         }
         else
            next = insert(current,next,n);
      }
   }
   
   printf("The list of elements : ");
   print(l);
   printf("\n");

   next = delete(current,next);

   printf("The list of elements after one delete : ");
   print(l);
   printf("\n");

   destroy(l);
   printf("List has been destroyed.  Bye bye.\n");

   return 0;
}

void print ( LIST *l )
{
   if (l != NULL)
   {
      printf(" %d", l->head);
      print(l->tail);
   }
}

LIST *create ( int n )
{
   LIST *l;

   l = (LIST*)calloc(1,sizeof(LIST));
   l->head = n;
   l->tail = NULL;

   return l;
}

LIST *insert ( LIST *current, LIST *next, int n )
{
   LIST *p;

   p = (LIST*)calloc(1,sizeof(LIST));
   p->head = n;
   p->tail = next;
   current->tail = p;
   next = p;

   return next;
}

LIST *delete ( LIST *current, LIST *next )
{
   current->tail = next->tail;
   free(next);
   return current->tail;
}

void destroy ( LIST *l )
{
   if (l != NULL)
   {
      destroy(l->tail);
      free(l);
   }
}