设计一个日期类date，其中包含年、月、日等数据成员。要求实现日期的基本运算，

如一日期加上天数、或减去天数后的日期，两个日期之间相差的天数。-Design a date class date, which includes members of the year, month, date, and other data. Required to achieve that the date of the basic operations, such as date plus the number of days, or subtracting the number of days after the date of the difference between the number of days between two dates.