自己写的表达式计算器，可以计算类似9+2-3*5*4/3-4+5*-2的表达式，只是计算数和运算符的最大个数必须先指定好，不能运算带括号的表达式

-Write your own expression calculator, can be calculated expression similar to 9+2-3*5*4/3-4+5*-2, the maximum number is calculated and the number of operators must first specify a good operation, not the bracketed expression