算术表达式与二叉树之间存在着对应关系，编写把以前缀形式输入的合法算术表达式转换为中缀表达式，再转换为后缀表达式，并求表达式的值-Arithmetic expressions with binary tree there is a correlation between the preparation of the form to enter the legitimate prefix arithmetic expression conversion infix expression, and then converted to suffix expressions and expressions for the value of