L-27 MCS 275 Mon 19 Mar 2001

/* L-27 MCS 275 Mon 19 Mar 2001 Count and lookup, insert and append */

#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 */

int rec_count ( LIST *l );
/* returns the number of elements in a list, recursively */
int itr_count ( LIST *l );
/* returns the number of elements in a list, iteratively */

int lookup ( LIST *l, int k, int n );
/* returns the position of n in the list l if n occurs in the list,
   otherwise -1 is returned; call lookup with k equal to one */

LIST *insert ( LIST *l, int n );
/* inserts the number n to the front of the list */

LIST *append ( LIST *first, LIST *last, int n );
/* appends the element n to the end of the list,
   returns the new pointer to the last element in the list */

int main()
{
   LIST *l,*first,*last;
   int n,ind;

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

   printf("Give element to search for : ");
   scanf("%d", &n);
   ind = lookup(l,1,n);
   if (ind < 0)
      printf("The number %d does not occur in the list.\n", n);
   else
      printf("The number %d occurs at position %d in the list.\n", n, ind);

   printf("Creating list of positive numbers with append...\n");
   first = NULL;
   last = NULL;
   for (;;)
   {
      printf("  Give a positive number (0 to stop) : ");
      scanf("%d", &n);
      if (n <= 0)
         break;
      else
      {
         last = append(first,last,n);
         if (first == NULL) first = last;
      }
   }
  
   printf("The list of %d elements : ", rec_count(first));
   print(first);
   printf("\n");


   return 0;
}

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

int rec_count ( LIST *l )
{
   if (l == NULL)
      return 0;
   else
      return 1 + rec_count(l->tail);
}

int itr_count ( LIST *l )
{
   LIST *p;
   int cnt=0;

   for (p = l; p != NULL; p = p->tail) cnt++;

   return cnt;
}

int lookup ( LIST *l, int k, int n )
{
   if (l == NULL)
      return -1;
   else if (l->head == n)
      return k;
   else
      return lookup(l->tail,k+1,n);
}

LIST *insert ( LIST *l, int n )
{
   LIST *p;

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

   return p;
}

LIST *append ( LIST *first, LIST *last, int n )
{
   LIST *p;

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

   if (first == NULL)
      last = p;
   else
   {
      last->tail = p;
      last = p;
   }

   return last;
}