c#编写的计算器，这个计算器是手动输入一般的加减乘除公式就可以计算，比如（3+2）*8/9就可以直接算出结果，不用一个个输入。-c# write calculator, this calculator is to manually enter the general formula of addition, subtraction can be calculated, such as (3+2)* 8/9 can directly calculate the result, not an inp