C++计算两个日期年月日的天数差值

可以使用以下代码计算两个日期之间的天数差值：

#include <iostream>
using namespace std;

int daysInMonth(int year, int month) {
    switch (month) {
        case 2:
            if (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)) {
                return 29;
            } else {
                return 28;
            }
        case 4:
        case 6:
        case 9:
        case 11:
            return 30;
        default:
            return 31;
    }
}

int daysBetweenDates(int year1, int month1, int day1, int year2, int month2, int day2) {
    int days = 0;
    if (year1 < year2 || (year1 == year2 && month1 < month2) || (year1 == year2 && month1 == month2 && day1 < day2)) {
        // Swap the dates so that (year1,month1,day1) is before (year2,month2,day2)
        swap(year1, year2);
        swap(month1, month2);
        swap(day1, day2);
    }
    while (year1 > year2 || (year1 == year2 && month1 > month2) || (year1 == year2 && month1 == month2 && day1 > day2)) {
        days += daysInMonth(year1, month1) - day1 + 1;
        day1 = 1;
        if (month1 == 12) {
            month1 = 1;
            year1--;
        } else {
            month1++;
        }
    }
    days += day2 - day1;
    return days;
}

int main() {
    int year1, month1, day1, year2, month2, day2;
    cout << "Enter the first date (yyyy mm dd): ";
    cin >> year1 >> month1 >> day1;
    cout << "Enter the second date (yyyy mm dd): ";
    cin >> year2 >> month2 >> day2;
    int days = daysBetweenDates(year1, month1, day1, year2, month2, day2);
    cout << "The number of days between the two dates is: " << days << endl;
    return 0;
}

这段代码会提示用户输入两个日期，然后调用 `daysBetweenDates` 函数计算它们之间的天数差值，并输出结果。`daysBetweenDates` 函数使用了一个 `daysInMonth` 函数来计算每个月的天数，然后使用一个循环来逐个月地累加天数直到达到第二个日期。