为日期定义一个类。属性为年、月、日。要求重载 “++”、“--”（自增和自减运算符要求分前置和后置）、“<<”、“>>”等运算符，实现今天日期的输入输出、明天、昨天的日期求解和输出。用C++多文件实现

以下是实现代码，分为Date.h和Date.cpp两个文件：

### Date.h

#pragma once

#include <iostream>

class Date {
public:
    Date(int y, int m, int d) : year(y), month(m), day(d) {}

    friend std::ostream& operator<<(std::ostream& os, const Date& date);
    friend std::istream& operator>>(std::istream& is, Date& date);

    Date operator++();   // 前置自增运算符
    Date operator++(int);  // 后置自增运算符
    Date operator--();   // 前置自减运算符
    Date operator--(int);  // 后置自减运算符

private:
    int year;
    int month;
    int day;
};

### Date.cpp

#include "Date.h"

#include <iomanip>

std::ostream& operator<<(std::ostream& os, const Date& date) {
    os << date.year << "-" << std::setw(2) << std::setfill('0') << date.month << "-" << std::setw(2) << std::setfill('0') << date.day;
    return os;
}

std::istream& operator>>(std::istream& is, Date& date) {
    char delimiter;
    is >> date.year >> delimiter >> date.month >> delimiter >> date.day;
    return is;
}

Date Date::operator++() {
    if (day == 31 && month == 12) {
        year++;
        month = day = 1;
    } else if (day == 31) {
        month++;
        day = 1;
    } else {
        day++;
    }
    return *this;
}

Date Date::operator++(int) {
    Date temp = *this;
    ++(*this);
    return temp;
}

Date Date::operator--() {
    if (day == 1 && month == 1) {
        year--;
        month = day = 31;
    } else if (day == 1) {
        month--;
        day = 31;
    } else {
        day--;
    }
    return *this;
}

Date Date::operator--(int) {
    Date temp = *this;
    --(*this);
    return temp;
}

使用示例：

#include "Date.h"

#include <iostream>

int main() {
    Date today(2021, 9, 1);
    std::cout << "Today is " << today << std::endl;

    Date tomorrow = today++;
    std::cout << "Tomorrow is " << tomorrow << std::endl;

    Date yesterday = today--;
    std::cout << "Yesterday was " << yesterday << std::endl;

    std::cout << "Enter a date (YYYY-MM-DD): ";
    std::cin >> today;
    std::cout << "You entered " << today << std::endl;

    return 0;
}