说明：  此代码可以根据用户对于日期的输入，进行对于日期的大小比较，月份的字母缩写和数字的转换。还能进行年月日的进位，并考虑了月份的天数。
(This assignment asks student to write a program with a class called “Date” in order to realize the following requirements: The class should contain three data members namely denoting the year, the 3-letter abbreviation of month and the data. Beside the basic fundamental requirements. Additionally, the program should involve operator overloading. For instance, the assignment operator “=” is aimed to assign the value of one Data object to the other. Comparator operator “>” “<” and “==” are initialized to compare two dates. Also, operator “++” is aimed to change date value to the next date. )