一个计算器示例:实现加、减、乘、除运算，注意在进行除法运算时，如果除数为0，那么【简单】就直接输出0来，【复杂】那么要对用户进行错误提示-Examples of a calculator: the realization of add, subtract, multiply, with the exception of computing, pay attention to during the division operation, if the divisor is 0, then a si