数学表达式求值
编写一个求解包括+、-、×、÷ 运算符的数学表达式值的程序，要求如下：
（1）具有操作界面；
（2）采用算符优先分析法求解数学表达式的值；
（3）可以测试多个数学表达式，每个数学表达式通过键盘输入，可以是合法的数学表达式，
也可以是不合法的数学表达式；
（4）如果数学表达式是合法的，则将数学表达式及其值保存到Mathematical-Expression.txt
文件中；否则将数学表达式及提示信息保存到Mathematical-Expression.txt 文件中，文件格
式示例如下：
数学表达式：16+2*3-14+7*2
值：22
数学表达式：3*+4/2
提示信息：数学表达式不合法
数学表达式：21-12/2+16-2*3+6/3
值：27(Evaluation of mathematical expressions
The preparation of a solution including +, -, *, / operator the mathematical expressions of the value of the program, the requirements are as follows:
(1) having operation interface;
(2) the operator priority analysis method is used to solve the mathematical expressions;
(3) you can test multiple mathematical expressions. Each mathematical expression is entered by keyboard. It can be a valid mathematical expression,
It can also be an illegal mathematical expression;
(4) if the mathematical expression is legal, the math expression and its values are saved to Mathematical-Expression.txt
In the file; otherwise, save the math expressions and prompt information into the Mathematical-Expression.txt file
Examples are as follows:
Mathematical expression: 16+2*3-14+7*2
Value: 22
Mathematical expression: 3*+4/2
Prompt information: mathematical expression is illegal
Mathematical expression: 21-12/2+16-2*3+6/3
Value: 27)