1．程序的功能：遍历一个二叉树并输出。 2．输入输出的要求：输入可以是单个数字，也可以是单个字符，以0结束。二叉树的遍历方式可以是前序，中序，后序，程序中用switch函数进行开关选择-1. The functionality : a binary tree traversal and output. 2. The input and output : input can be a single figure, it could be a single character to the end of 0. The binary tree traversal mode can be pre-sequence, sequence after sequence, procedures used switch function for switching options