#include<stdio.h>

// integer linked lists:

typedef struct cell * cellp;
struct cell
{
   int head;
   struct cell * tail;
};


// constructor:
struct cell* cons(int h, struct cell* t)
{
   struct cell * thiscell;
   thiscell = (struct cell*)malloc(sizeof(struct cell));
   thiscell->head = h;
   thiscell->tail = t;
   return thiscell;
}

// accessors:
int car(cellp l)
{
   if (l!=NULL) return l->head; 
     else { printf("error\n"); return 0; }
}

struct cell* cdr(cellp l)
{
   if (l!=NULL) return l->tail; 
     else return NULL;
}

// cons(2,cons(4,cons(6,NULL)));

int length(struct cell* l) 
{
   struct cell* i;
   int ax = 0; // accumulator
   for(i=l;i!=NULL;i=cdr(i)) ax++;
   return ax;
}

// returns nth cell, 0th is first.
struct cell* nth(struct cell* l, int n)
{
  if (n<1) return l; else return nth(cdr(l),n-1);
}

// return last cell
struct cell* last(struct cell* l)
{
      struct cell* i = l;
      if (i==NULL) return NULL;
      while(cdr(l) != NULL) i = cdr(i);
      return i;
}

void printlist(cellp l)
{
 if (l==NULL) printf("\n"); else
     { printf("%d ",car(l)); printlist(cdr(l)); }
}


int main()
{
  cellp A;  cellp B;  cellp C;
  A = cons(1,cons(3,cons(5,cons(7,NULL))));
  B = cons(2,cons(4,cons(6,cons(8,NULL))));
  C = cons(car(A),cdr(B));  // C now shares structure with B

  // if B is deallocated here, C will be destroyed too!

  //  A = cons(0,A);
  printlist(A);
  printf("%d\n",length(B));
  exit(0);
}