代碼：

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int hashMapping(int mouth)
{
    vector<int> days{31,28,31,30,31,30,31,31,30,31,30,31};
    return days[mouth - 1];
}

int IsLeapYear(int year, int mouth)
{
    if(((year%4 == 0 && year%100 != 0) || (year%400 == 0)) && mouth == 2)
    {
        return hashMapping(mouth) + 1;
    }
    return hashMapping(mouth);
}

int CalculateDays(int start_year, int end_year, int start_mouth, int end_mouth)
{
    int days = 0;
    if (end_mouth >= start_mouth)
    {
        if (start_year < end_year)
        {
            for (int i = start_year; i < end_year; i++)
            {
                for (int j = start_mouth; j <= 12; j++)
                    days += IsLeapYear(i, j);
                for (int j = 1; j <= end_mouth; j++)
                    days += IsLeapYear(i, j);
            }
        }
        else
        {
            for (int j = start_mouth; j <= end_mouth; j++)
                days += IsLeapYear(start_year, j);
        }
    }
    else
    {
        for (int i = start_year; i < end_year; i++)
        {
            for (int j = start_mouth; j <= 12; j++)
                days += IsLeapYear(i, j);
            for (int j = 1; j <= end_mouth; j++)
                days += IsLeapYear(i, j);
        }
    }

    return days;
}

string hashFunc(int days, int week)
{
    vector<string> str{"星期一","星期二","星期三","星期四","星期五","星期六","星期天"};
    return str[(week - 1 + days%7)%7];
}

void PrintWeek(int start_year, int start_mouth, int start_day, int week, int end_year, int end_mouth, int end_day)
{
    string we;
    int days;
    switch(week)
    {
        case 1:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 2:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 3:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 4:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 5:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 6:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
        case 7:
            days = CalculateDays(start_year, end_year, start_mouth, end_mouth) - (start_day + IsLeapYear(end_year, end_mouth) - end_day);
            we = hashFunc(days, week);
            break;
    }
    cout << start_year << ‘/‘ << start_mouth << ‘/‘ << start_day <<
        ‘~‘ << end_year << ‘/‘ << end_mouth << ‘/‘ << end_day << " 共有:"
        << days << "天 " << endl;
    cout << end_year << "年" << end_mouth << "月" << end_day << "日是" << we << endl;
}

int main()
{
    int start_year, start_mouth, start_day;
    int end_year, end_mouth, end_day;
    int week;

    cout << "請輸入起始年/月/日 以及 星期幾：" << endl;
    cin >> start_year;
    cin >> start_mouth;
    cin >> start_day;
    cin >> week;

    cout << "請輸入結束年/月/日：" << endl;
    cin >> end_year;
    cin >> end_mouth;
    cin >> end_day;

    PrintWeek(start_year, start_mouth, start_day, week, end_year, end_mouth, end_day);

    return 0;
}

　　運行結果：

C/C++ - 實現計算 今天是xx年xx月xx日 星期x 請問xx年xx月xx日是星期幾?