引言： 数的代码实现， 先序遍历、中序、后序、层次遍历

/* binary_tree.h */
#ifndef _BINARY_TREE_H
#define _BINARY_TREE_H

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

#define DEBUG(msg) \
	printf("--%s--, %s\n", __func__, msg);

typedef char data_t;
typedef struct node {
	data_t data;
	struct node *lnext, *rnext;
}bitree_t;


bitree_t *binary_tree_create();
void preorder(bitree_t *r);
void inorder(bitree_t *r);
void postorder(bitree_t *r);

#endif

/* binary_tree.c */
#include "binary_tree.h"

bitree_t *binary_tree_create()
{
	char ch;
	bitree_t *root = NULL;

	scanf("%c", &ch);
	if(ch == '#')
		return NULL;

	root = (bitree_t *)malloc(sizeof(bitree_t));
	if(root == NULL) {
		DEBUG("malloc failed");	
		return NULL;
	}

	root->data = ch;
	root->lnext = binary_tree_create();
	root->rnext = binary_tree_create();

	return root;
}

void preorder(bitree_t *r)
{
	if(r == NULL) {
		return ;
	}
	printf("%c ", r->data);
	preorder(r->lnext);
	preorder(r->rnext);
	
}

void inorder(bitree_t *r)
{
	if(r == NULL) {
		return ;
	}
	inorder(r->lnext);
	printf("%c ", r->data);
	inorder(r->rnext);
	
}

void postorder(bitree_t *r)
{
	if(r == NULL) {
		return ;
	}

	postorder(r->lnext);
	postorder(r->rnext);
	printf("%c ", r->data);
	
}

/* test.c */
#include "binary_tree.h"

int main(int argc, const char *argv[])
{

	bitree_t *r;

	r = binary_tree_create();

	preorder(r);
	puts("");

	inorder(r);
	puts("");

	postorder(r);
	puts("");

	return 0;
}