计算器，可以转换模式，可以加减乘除，可以取余，可以加括号-Calculator, can change, can add, subtract, multiply and divide

实现加减乘除，阶乘累加的多功能计算器,对于初学者是很好的练习程序。-Beginners a simple function of small software, realize the add, subtract, multiply and divide, factorial function.

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