C++ Bjarne Stroustrup PPP-第9章钻取4-库特枚举错误

我正在努力解决比亚恩·斯特劳斯特鲁普斯《原则与实践》第二版的第4次练习。出于某种原因，它不会让我忘记我之前初始化的月份和年份成员。我知道使用枚举数还有其他选择，但我想知道如何使用它。有人能帮我吗？干杯

//  Philipp Siedler
//  Bjarne Stroustrup's PPP
//  Chapter 9 Drill 4

#include "std_lib_facilities.h"

class Year {
    static const int min = 1800;
    static const int max = 2200;
private:
    int y;
public:
    class Invalid {};
    Year(int x) : y{ x } { if (x < min || max <= x) throw Invalid{}; };
    int year() { return y; };
};

enum class Month {
    jan = 1, feb, march, apr, may, jun, jul, aug, sep, oct, nov, dec
};

class Date {
private:
    Year y;
    Month m;
    int d;
public:
    Date(Year y, Month m, int d) : y(y), m(m), d(d) {};
    Year year() { return Year{ y }; };
    Month month() { return Month{ m }; };
    int day() { return d; };
    void add_day(int n);
};

void Date::add_day(int n) {
    d += n;
}

int main()
try
{
    Date today{ Year{ 1978 }, Month::jun, 25 };
    Date tomorrow = today;

    tomorrow.add_day(1);

    cout << "Year: " << today.year() << " Month: " << today.month() << " Day: " << today.day() << "\n";
    cout << "Year: " << tomorrow.year() << " Month: " << tomorrow.month() << " Day: " << tomorrow.day() << "\n";

    keep_window_open();
}

catch (runtime_error e) {
    cout << e.what() << '\n';
    keep_window_open();
}
catch (...) {
    cout << "Exiting" << '\n';
    keep_window_open();
}

//Philipp Siedler
//比亚恩·斯特劳斯图普的PPP
//第9章练习4
#包括“std_lib_facilities.h”
学年{
静态常数int最小值=1800；
静态常数int max=2200；
私人：
int-y；
公众：
类无效{}；
Year（int x）：y{x}{if（x
//  Philipp Siedler
//  Bjarne Stroustrup's PPP
//  Chapter 9 Drill 4

#include "std_lib_facilities.h"

class Date {
public:
    enum Month {
        jan = 1, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec
    };

    Date(int y, Month m, int d);
    void add_day(int n);

    int year() const { return y; }
    Month month() const { return m; }
    int day() const { return d; }

private:
    int y;
    Month m;
    int d;
};

Date::Date(int y0, Date::Month m0, int d0) {
    d = d0;
    m = m0;
    y = y0;
}

void Date::add_day(int n) {
    d += n;
}

static ostream & operator<< (ostream & os, const Date::Month & m) {
    switch (m) {
    case Date::jan: os << "January"; break;
    case Date::feb: os << "February"; break;
    case Date::mar: os << "March"; break;
    case Date::apr: os << "April"; break;
    case Date::may: os << "May"; break;
    case Date::jun: os << "June"; break;
    case Date::jul: os << "July"; break;
    case Date::aug: os << "August"; break;
    case Date::sep: os << "September"; break;
    case Date::oct: os << "October"; break;
    case Date::nov: os << "November"; break;
    case Date::dec: os << "December"; break;
    }
    return os;
}

ostream & operator<< (ostream & os, const Date & dd) {
    os << "Year: " << dd.year() << " Month: " << dd.month() << " Day: " << dd.day() << endl;
    return os;
}

int main()
try
{
    Date today{ 1978, Date::jun, 25 };
    Date tomorrow = today;
    tomorrow.add_day(1);

    cout << today;
    cout << tomorrow;

    keep_window_open();
}

catch (runtime_error e) {
    cout << e.what() << '\n';
    keep_window_open();
}
catch (...) {
    cout << "Exiting" << '\n';
    keep_window_open();
}

//Philipp Siedler
//比亚恩·斯特劳斯图普的PPP
//第9章练习4
#包括“std_lib_facilities.h”
上课日期{
公众：
枚举月{
一月=1，二月，三月，四月，五月，六月，七月，八月，九月，十月，十一月，十二月
};
日期（整数y、月份m、整数d）；
无效添加日（整数n）；
int year（）常量{return y；}
Month Month（）常量{return m；}
int day（）常量{return d；}
私人：
int-y；
月m；
int d；
};
日期：：日期（整数y0，日期：：月份m0，整数d0）{
d=d0；
m=m0；
y=y0；
}
作废日期：：添加日（整数n）{
d+=n；
}
静态的Oracle和操作程序No.<代码> STD:：FLASH  ING？我对代码和C++是新的，没有触及STD的主题：：Flash。Philipp Siedler。你必须重载操作员的错误：<代码> max @ JavaSun是的，谢谢。但是这不是我要问的问题。