实现了用树建立数值表达式，并求其值，随便输出它的广义表、前缀表达式和后缀表达式-To realize the tree is to develop a numerical expression, and for its value, literally output its generalized list, prefix and postfix expression expression

编写语义分析程序，实现对算术表达式的类型检查和求值。要求所分析的算术表达式由如下文法产生： E->E+T | E-T | T T->T*F | T/F | F F-> id | (E) | num -Write semantic analysis procedures, to achieve the type checking and arithmetic expressions are evaluated. Requirements analysis a