求算术表达式的结果，先输入一个四则运算规则（包括乘方）的表达式，然后计算其结果-arithmetic expression for the results to input a four Operational rules (including involution) of the expression, and then calculate the results

完成标准中缀算术表达式到后缀表达式的自动转换。-completed standard grade arithmetic expression of the suffix expression of an automatic conversion.

编写一个程序，通过前缀表达式来构造一个与之对应的算术表达式并存入二叉树中，通过中序遍历二叉树输出表达式及对其进行变量赋值，通过后序遍历二叉树计算表达式的值。(A program is written by prefix expression to construct an arithmetic expression corresponding to it and store it into two binary tree. Through traversing two fork tree out