C++ 计算任意两个日期之间的天数

C++写的一个计算两个日期之间天数的小程序：

#include <Windows.h>
#include <stdio.h>


struct tagDate
{
    int year;
    int month;
    int day;
};

//设置日期
void SetDate(int y, int m, int d, tagDate *date)
{
    date->year = y;
    date->month = m;
    date->day = d;
}

//是否闰年
int IsLeapYear(int year)
{
    return ((year%4==0) && (year%100!=0)||year%400==0);
}

//得到date.month的最大天数
int GetLastDay(tagDate date)
{
    int num;
    switch(date.month)
    {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
        num=31;
        break;
    case 2:
        num = 28+IsLeapYear(date.year);
        break;
    default:
        num = 30;
    }
    return num;
}

//日期是否合法
int IsDateValid(tagDate date)
{
    if(date.year <0 || date.month <1 || date.month> 12)
        return 0;

    if(date.day <1 || date.day> GetLastDay(date))
        return 0;

    return 1;
}

//date+1
void AddDay(tagDate *date)
{
    date->day++;
    if(date->day > GetLastDay(*date))
    {
        date->day = 1;
        date->month++;
        if(date->month > 12)
        {
            date->month = 1;
            date->year++;
        }
    }
}

//date1比date2小返回值为1，否则为0
int Compare(tagDate date1, tagDate date2)
{
    if(date1.year < date2.year)
        return 1;
    if(date1.year <= date2.year && date1.month < date2.month)
        return 1;
    if(date1.year <= date2.year && date1.month <= date2.month && date1.day < date2.day)
        return 1;

    return 0;
}
//计算两个日期的间隔天数
long DateDiff(tagDate date1, tagDate date2)
{
    long delta = 0;
    tagDate date3;
    //若date1 > date2,交换date1,date2
    if(!Compare(date1, date2))
    {
        date3 = date2;
        date2 = date1;
        date1 = date3;
    }

    //date1比date2少时，date1日期加1
    while(Compare(date1,date2))
    {
        AddDay(&date1);
        delta++;
    }
    return delta;
}

void main()
{
    tagDate date1, date2;
    int y, m, d;

    system("cls");
    while(1)
    {
        puts("
Input   date1	 ");
        scanf("%d,%d,%d", &y, &m, &d);
        SetDate(y, m, d, &date1);
        if(!IsDateValid(date1))
        {
            puts( "date1   is   invalid !");
            exit(1);
        }

        puts("
Input   date2	 ");
        scanf("%d,%d,%d", &y, &m, &d);
        SetDate(y, m, d, &date2);
        if(!IsDateValid(date2))
        {
            puts( "date2   is   invalid !");
            exit(1);
        }
        //
        printf("
Result : [%ld]", DateDiff(date1,date2));
    }
}

https://blog.csdn.net/hellokandy/article/details/52194332