程序代码：

#include <iostream>
using namespace std;
enum {YEAR = 2000 , MONTH = 1 , DAY = 1 , WEENDAY = 6};
class CDateTime
{
    int m_iYear;
    int m_iMonth;
    int m_iDay;
    int m_iHour;
    int m_iMinute;
    int m_iSecond;
public:
    CDateTime();
    CDateTime(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond);
    void SetDateTime(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond);
    
    void GetMonthFirstDayWeek(char * szTmp);//某个月第一天是星期几
    void DayToDay(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond);//两个时间相隔多少天
    CDateTime GetNextDay();//某一天的下一天是几号
    void GetWeekDayInfo(int iWeenDay , char * pszInfo);//求某年某月的第几周是哪几天
    
    void GetShowWeekDay(char * pszInfo);//显示那个周有哪几天
    void GetShowToDay();//显示私有变量天
    
private:
    int DayNum(int iYear=YEAR, int iMonth=MONTH, int iDay=DAY);//与初始值相隔的天数
    int GetYearDays();//求年有多少天
    int GetMonthDays();//求月份有多少天
    bool bRunYear();//计算闰年    
    int WeenDay();//计算周数
};

CDateTime::CDateTime()
{
    m_iYear = 0;
    m_iMonth = 0;
    m_iDay = 0;
    m_iHour = 0;
    m_iMinute = 0;
    m_iSecond = 0;
    
}

CDateTime::CDateTime(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond)
{
    m_iYear = iYear;
    m_iMonth = iMonth;
    m_iDay = iDay;
    m_iHour = iHour;
    m_iMinute = iMinute;
    m_iSecond = iSecond;
}

void CDateTime::SetDateTime(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond)
{
    m_iYear = iYear;
    m_iMonth = iMonth;
    m_iDay = iDay;
    m_iHour = iHour;
    m_iMinute = iMinute;
    m_iSecond = iSecond;
}

bool CDateTime::bRunYear()//判断闰年
{
    if (m_iYear % 4 == 0 && m_iYear % 100 != 0 || m_iYear % 100 ==0 && m_iYear % 400 ==0)
    {
        return true;
    }
    else
    {
        return false;
    }
}

int CDateTime::GetYearDays()//计算一年多少天
{
    int iTmp;
    if (bRunYear())
    {
        iTmp = 366;
    }
    else
    {
        iTmp = 365;
    }
    return iTmp;
}

int CDateTime::GetMonthDays()//计算一个月多少天
{
    int iMonth[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
    if (bRunYear())
    {
        iMonth[1] = 29;
    }
    return iMonth[m_iMonth - 1];
}

int CDateTime::DayNum(int iYear, int iMonth, int iDay)//判断输入与初始年份相差多少天
{
    int iTmp = 0 , i;
    CDateTime cDayNum;
    for (i = iYear; i < m_iYear; ++i)
    {        
        cDayNum.SetDateTime(i,0,0,0,0,0);
        iTmp += cDayNum.GetYearDays();
    }
    for (i = 1; i < m_iMonth; ++i)
    {
        cDayNum.SetDateTime(m_iYear,i,0,0,0,0);
        iTmp += cDayNum.GetMonthDays();
    }
    iTmp += m_iDay;
    ////////////////开始计算多出来的天数//////////////注：如果起始月日是1月1号的话这段可以不要~////

    if (iMonth > 1)
    {
        for (i = 1; i < iMonth; ++i)
        {
            cDayNum.SetDateTime(iYear,i,0,0,0,0);
            iTmp -= cDayNum.GetMonthDays();            
        }        
    }
    
    if (iDay > 1)
    {
        iTmp -= iDay;
    }     
    

    /////////////////减掉多出来的天数/////////////////////
    return iTmp;
}

int CDateTime::WeenDay()
{
    int iTmpDay = 0 , iTmpWeenday = WEENDAY - 1 , Tmp;
    int weenday[7] = {1,2,3,4,5,6,7};
    while (iTmpDay < DayNum())
    {
        if (iTmpWeenday > 6)//如果大于周日则返回周一
        {
            iTmpWeenday = 0;
        }
        Tmp = iTmpWeenday;
        ++iTmpWeenday;
        ++iTmpDay;        
    }
    return Tmp;
}

void CDateTime::GetMonthFirstDayWeek(char * szTmp)
{
    
    switch (WeenDay())
    {
    case 0: 
        strcpy(szTmp , "星期一");
        break;
    case 1:
        strcpy(szTmp , "星期二");
        break;
    case 2:
        strcpy(szTmp , "星期三");
        break;
    case 3:
        strcpy(szTmp , "星期四");
        break;
    case 4:
        strcpy(szTmp , "星期五");
        break;
    case 5:
        strcpy(szTmp , "星期六");
        break;
    case 6:
        strcpy(szTmp , "星期日");
        break;
    }
    
}

void CDateTime::DayToDay(int iYear, int iMonth, int iDay, int iHour, int iMinute, int iSecond)
{
    int iTmpDay = DayNum(iYear , iMonth , iDay) - 1;//求出间隔天数
    if (m_iSecond < iSecond)//如果结束秒小于起始秒
    {
        m_iSecond = 60 - iSecond + m_iSecond;//减去起始秒多出来的，然后再加结束秒
        --m_iMinute;//结束分钟减一
    }
    else
    {
        m_iSecond -= iSecond;
    }
//-------------水平分割线-------------------
    if (m_iMinute < iMinute)
    {
        m_iMinute = 60 - iMinute + m_iMinute;//减去起始分多出来的，然后再加结束分
        --m_iHour;//结束小时减一
    } 
    else
    {
        m_iMinute -= iMinute;
    }
//-------------水平分割线-------------------
    if (m_iHour < iHour)
    {
        m_iHour = 24 - iHour + m_iHour;//减去起始时多出来的，然后再加结束时
        --iTmpDay;//间隔天数减1
    } 
    else
    {
        m_iHour -= iHour;
    }
    
    cout << "您输入的这两个日期相差" << iTmpDay << "天" << m_iHour << "时" << m_iMinute << "分" << m_iSecond << "秒" << endl; 
}

CDateTime CDateTime::GetNextDay()
{
     int iMonth = GetMonthDays();
    ++m_iDay;
    if (m_iDay > iMonth)
    {
        m_iDay = 1;
    }

    CDateTime objTmp;
    objTmp.m_iDay = m_iDay;
    return objTmp;
}
void CDateTime::GetShowToDay()
{
    cout << "下一天是" << m_iDay<< endl;
}

void CDateTime::GetWeekDayInfo(int iWeenDay , char * pszInfo)
{
    int iTmp = 0 , iTmpDay = 0;

     CDateTime cWeenDay;
    for (int i = 0; i < GetMonthDays(); ++i)
    {
        cWeenDay.SetDateTime(m_iYear,m_iMonth,i,0,0,0);
        if (cWeenDay.WeenDay() == 0)//如果等于周一，则第一个周开始
        {
            ++iTmp;
        }
        if (iTmp==iWeenDay)//如果等于当前周
        {
            *(pszInfo + iTmpDay) = char(i+48);        
            ++iTmpDay;
        }

    }
    *(pszInfo + iTmpDay)='\0';
}
void CDateTime::GetShowWeekDay(char * pszInfo)
{
    for (int i = 0; i < strlen(pszInfo); ++i)
    {
        cout << *(pszInfo + i) << endl;
    }

}

int main()
{
    int iYear , iMonth , iDay , iweenday;
    cout << "-------------------黄金分割线----------------------------" << endl;
    cout << "求某个月的第一天是星期几" << endl;
    cout << "请输入年：";
    cin >> iYear;
    cout << "请输入月：";
    cin >> iMonth;
    CDateTime Fist(iYear , iMonth , 1 , 0 , 0 , 0);
    char szTmp[10];
    Fist.GetMonthFirstDayWeek(szTmp);
    cout << iYear << "年" << iMonth << "月" << "的第一天是：" << szTmp << endl;
    cout << "-------------------黄金分割线----------------------------" << endl;
    int iStarYear , iStarMonth , iStarDay , iStarHour , iStarMinute , iStarSecond;
    cout << "求两个时间相隔多少天" << endl;
    cout << "请输入起始年：";
    cin >> iStarYear;
    cout << "请输入起始月：";
    cin >> iStarMonth;
    cout << "请输入起始日：";
    cin >> iStarDay;
    cout << "请输入起始时：";
    cin >> iStarHour;
    cout << "请输入起始分：";
    cin >> iStarMinute;
    cout << "请输入起始秒：";
     cin >> iStarSecond;
    int iLastYear , iLastMonth , iLastDay , iLastHour , iLastMinute , iLastSecond;
    cout << "请输入结束年：";
    cin >> iLastYear;
    cout << "请输入结束月：";
    cin >> iLastMonth;
    cout << "请输入结束日：";
    cin >> iLastDay;
    cout << "请输入结束时：";
    cin >> iLastHour;
    cout << "请输入结束分：";
    cin >> iLastMinute;
    cout << "请输入结束秒：";
     cin >> iLastSecond;
    CDateTime Two(iLastYear , iLastMonth , iLastDay , iLastHour , iLastMinute , iLastSecond);
    Two.DayToDay(iStarYear , iStarMonth , iStarDay , iStarHour , iStarMinute , iStarSecond);
    cout << "-------------------黄金分割线----------------------------" << endl;
    
    cout << "求某天的下一天是几号" << endl;
    cout << "请输入年：";
    cin >> iYear;
    cout << "请输入月：";
    cin >> iMonth;
    cout << "请输入日：";
    cin >> iDay;
    CDateTime Three(iYear , iMonth , iDay , 0 , 0 , 0);
    CDateTime objTmp;
    objTmp = Three.GetNextDay();
    objTmp.GetShowToDay();

    cout << "-------------------黄金分割线----------------------------" << endl;

    cout << "求某年某月的第几周是哪几天" << endl;
    cout << "请输入年：";
    cin >> iYear;
    cout << "请输入月：";
    cin >> iMonth;
    cout << "请输入第几周：";
    cin >> iweenday;
    CDateTime Four(iYear , iMonth , 1 , 0 , 0 , 0);
    char szT[100];
    Four.GetWeekDayInfo(iweenday , szT);    
    Four.GetShowWeekDay(szT);
    return 0;
}