计算两个日期之间相差的天数，时间之间相差的小时数-The difference between the number of days between two dates

使用C++语言构造一个日期时间类(Timedate)，并完成测试(成员函数和普通函数) -Using c++ language constructs a date/time class (Timedate), and complete the test (member functions and common function)