重言式判别 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；-Tautologies determine a logical expression of its argument, if for any kind of values are true, then known as the tautology

用c++编写的用栈模拟pc真实进行表达式计算的过程-Written with c++ using stack to simulate pc real expression evaluates

PCRE (Perl Compatible Regular Expression) Usage Example