C++ 计算任意两个日期之间的天数

#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("\nInput   date1\t ");
scanf("%d,%d,%d", &y, &m, &d);
SetDate(y, m, d, &date1);
if(!IsDateValid(date1))
{
puts( "date1   is   invalid !");
exit(1);
}

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