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。

-Customize a simple date class DateType, it has a data member y, m, d, is used to indicate the current date, month, and day. To achieve the latter design class (complete) function, and then design the appropriate class member functions. For example, the following is the " prototype"　is used to achieve the increase of day, compare two date are equal, and the output of dates and other operations. Please complete all kinds of member functions, and prepare the main function, indicating DateType class object for each member function definition be called to verify their correctness.