可以检查用户输入表达式是否正确的计算器，用户输入表达式（任意），通过判断表达式的正确与否给出相应的提示或者给出值，并记录在文件中方便查询-You can check whether the user entered the correct expression calculator, the user input expression (arbitrary), by judging whether or not to give the correct expression

Prompt or the corresponding value is given, and recorded in the files easier to find