一个不带界面的计算器，用户只需要在文本文件input.txt中输入计算表达式，即可通过运行程序得到结果，输出在output.txt中；

支持加减乘除，取余数，乘方，括号等等；

如：5+4 = 输出9

5+4*4+9/3 = 输出24

(5+4)*4+9/3 = 输出39

(50+4)*(40 3)+288/(147-3) = 输出56

(50+4)^2*(40 3)+288/(147-3) = 输出2918-Interface without a calculator, the user need only enter a text file input.txt expressions, you can get results by running the program, the output in the output.txt　support calculation, check the balance, involution, brackets etc.　such as: 5+4 = 9 5+4 Output* 4+9/3 = output 24 (5+4)* 4+9/3 = output 39 (50+4)* (40　3)+288/(147-3) = output 56 (50+4) ^ 2* (40　3)+288/(147-3) = output 2918