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

struct NODE_STRUCT {
  char value;
  struct NODE_STRUCT* lch;   /* link to left child */
  struct NODE_STRUCT* rch;   /* link to right child */
};

typedef struct NODE_STRUCT NODE;
typedef struct NODE_STRUCT* PNODE;

#define merror() {printf("memory allocation error\n");exit(1);}

/* function Insert -------------------------------------------- */
NODE Insert(PNODE n,char c)
{
  if (n == NULL) {  /* at the end of path, or tree not built yet */
    if ((n = malloc(sizeof(NODE))) == NULL) merror();
    n->value = c;
    n->lch = n->rch = NULL;
    return n;
  }
  if (c < n->value)  /* go left */
    n->lch = Insert(n->lch,c);
  else               /* go right */
    n->rch = Insert(n->rch,c);
  return n;
}/*end Insert*/


/* function Show ---------------------------------------------- */
void Show(PNODE n)
{
  if (n == NULL) return;
  Show(n->lch);
  printf(" %c",n->value);
  Show(n->rch);
}/*end Show*/