表达式判别，输入一个算术式子，先判别它是否正确，然后计算。-The expression of discrimination, enter an arithmetic expression, to determine whether it is correct, then calculate.

表达式的解析,主要是算术表达式的分析,分析成四元式,不错的(Expression parsing, mainly is the analysis of the arithmetic expression analysis into four yuan, pretty good)