定义一个有理数类，属性有分子、分母 用成员函数重载 == 重载前缀++ 后缀++ (member function 或 friend function 均可 ) 重载 >> << 自己写 main 对有理数类进行测试 -Define a rational number class, property has numerator, denominator == overloaded with members of the function ov