2.　　自定义一个简单的日期类DateType，它具有数据成员y、m、d，用来表示当前日期的年、月、日。而后设计该类欲实现（完成）的功能，进而设计出相应的类成员函数。

例如，下面给出的“雏形”可用来实现对天的增加，比较两个日期是否相等，以及对日期的输出等操作。请完成各类成员函数，并编制主函数，说明DateType类对象，对定义的各成员函数进行调用，以验证它们的正确性。

-2. Since the date of the definition of a simple class DateType, it has a data member y, m, d, is used to indicate the current date of the year, month, day. And then design the class is to be achieved (completed) functions, and then design the appropriate class member functions. For example, the following is given a " prototype"　can be used to realize an increase in days to compare two dates are equal, and the output of the date of such an operation. Please complete the various forms of membership functions, and the preparation of the main function, indicating DateType class objects, the definition of the various members of the function call to verify their correctness.