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;
}