一:需求分析

1．本程序需掌握树和二叉树的概念及工作原理，运用其原理及概念完成实验.。

2．问题描述：

一个逻辑表达式如果对于其变元的任一种取值都为真，则称为重言式；反之，如果对于其变元的任一种取值都为假，则称为矛盾式；然而，更多的情况下，既非重言式，也非矛盾式。试写一程序，通过真值表判断一个逻辑表达式属于那一类。

3．基本要求：

（1）逻辑表达式从终端输入，长度不超过一行。逻辑运算符包括“|”，“&”和“~”,

分别表示或、与和非，运算优先程度递增，但可以有括号改变，即括号内的运算优先。逻辑变元为大写字母。表达式中任何地方都可以含有多个空格符。

（2）若是重言式或矛盾式，可以只“显示True forever”或“False forever”，否则显示“Satisfactible”以及变量名序列，与用户交互。若用户对表达式中变元取一组值，程序就求出并显示逻辑表达式的值。

-1 : a needs analysis. The process required the trees and the binary tree master the concept and principle, to use its principles and the concept of completion of the pilot. . 2. Problem descr iption : If a logical expression for the changes in the yuan's value for a true, as tautology; Instead, If the changes for the yuan's value for a fake, then called the contradiction; However, the more the situation, neither tautology. is not a contradiction. Try to write a procedure for the adoption of a truth table judgment logical expression belong into that category. 3. Basic requirements : (a) logical expression from the terminal input, not longer than his. Logical Operators including "|","