说明：  偶写了个将中序表达式转化成后序表达式的程序。不过只能对单字符进行操作，现在改良了一下，能够对任意精度的数值进行运算，并且能够处理任意多的括弧（不过我并没有显式的允许输入[]或者{}，只要将它们都成（）就可以实现[]或者是{}的操作了），由于程序中间有小数点，所以在写成后序的时候，为了以便于区分输入的数据，我用下划线将它们隔离了开来。
(even wrote a sequence of Chinese expressions into expressions sequence after the procedure. But only on single characters for operation, now improved a bit to be able to arbitrary accuracy of numerical calculations. and to be able to handle any number of brackets (although I do not have explicit permission or input [] (), as long as they are 10% () can be achieved [] () or the operation of), since there is a decimal point procedures, Therefore, the completion of the sequence of time, in order to in order to distinguish between data entry, I used them to underscore the isolation years.)