C语言小程序（三）、判断两个日期之差

输入两个日期，计算之间相差多少天。 用了两种方法实现，第二种利用结构体，代码比较清晰，其余的都一样。

1.普通的写法

#include <stdio.h>

int leapyear(int year)
{
	if((year%4==0 && year%100!=0) || year%400==0)
		return 1;
	else
		return 0;
}

int days(int *day1, int *day2)
{
	int i=0;
	int *tmp;
	int diff = 0;
	const int month[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
	if(day1[0] == day2[0])
	{
		if(day1[1] == day2[1])
		{
			diff = day1[2] - day2[2];
			diff = (diff < 0)?(-diff):diff;
		}
		else
		{
			if(day1[1] < day2[1])				//day1=1991-5-8   day2=1991-6-2
			{
				tmp = day1;						//day1=1991-6-2   day2=1991-5-8
				day1 = day2;
				day2 = tmp;
			}
			for(i=day2[1]+1; i<day1[1]; i++)
			{
				diff +=  month[i];
			}
			diff += month[day2[1]] - day2[2] + day1[2];
			if(day2[1] <= 2 && day1[1] >2)
				if(leapyear(day2[0]))
					diff++;
		}
	}
	else
	{
		if(day1[0] < day2[0])
		{
			tmp = day1;
			day1 = day2;
			day2 = tmp;
		}
		for(i=day2[0]+1; i<day1[0]; i++)
		{
			if(leapyear(i))
				diff += 366;
			else
				diff += 365;
		}
		for(i=day2[1]+1; i<=12; i++)					//day1=1992-1-1   day2=1991-1-1
		{
			diff += month[i];
		}
		diff += (month[day2[1]] - day2[2]);
		if(day2[1] <= 2)
			if(leapyear(day2[0]))
				diff++;
		for(i=1; i<day1[1]; i++)
		{
			diff += month[i];
		}
		diff += day1[2];
		if(day1[1] > 2)
			if(leapyear(day1[0]))
				diff++;
	}

	return diff;
}

int main()
{
	int day1[3], day2[3];
	int day = 0;
	printf("输入日期：");
	scanf("%d-%d-%d",&day1[0], &day1[1], &day1[2]);
	printf("输入另一个日期：");
	scanf("%d-%d-%d",&day2[0], &day2[1], &day2[2]);
	day = days(day1, day2);
	printf("两个日期之间共有%d天。\n",day);

	return 0;
}

2.利用结构体，代码更整洁一些

#include <stdio.h>

typedef struct date
{
	int year;
	int month;
	int day;
}DATE; 

int leapyear(int year)
{
	if((year%4==0 && year%100!=0) || year%400==0)
		return 1;
	else
		return 0;
}

int compare(DATE *d1, DATE *d2)				//如果第一个日期比第二个日期大，交换日期
{
	DATE *tmp;
	if(d1->year == d2->year)				//年数相等
	{
		if(d1->month > d2->month)			//月数相等
		{
			tmp = d1;
			d1 = d2;
			d2 = d1;
		}
		else if(d1->month == d2->month)		//日期相等
		{
			if(d1->day > d2->day)
			{
				tmp = d1;
				d1 = d2;
				d2 = d1;
			}
		}
	}
	else if(d1->year > d2->year)
	{
		tmp = d1;
		d1 = d2;
		d2 = tmp;
	}

	return 0;
}

int diff(DATE *date1, DATE *date2)
{
	int i;
	int diff = 0;
	const int month[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
	if(date1->year == date2->year)
	{
		if(date1->month == date2->month)
		{
			diff = date2->day - date1->day;
		}
		else
		{
			for(i=date1->month+1; i<date2->month; i++)
			{
				diff += month[i];
			}
			diff += month[date1->month] - date1->day + date2->day;
			if(leapyear(date1->year))
				if(date1->month <=2 && date2->month >2)
					diff++;
		}
	}
	else
	{
		for(i=date1->year+1; i<date2->year; i++)
		{
			if(leapyear(i))
				diff += 366;
			else
				diff += 365;
		}
		for(i=date1->month+1; i<=12; i++)				//date1距离年末多少天
		{
			diff += month[i];
		}
		diff += month[date1->month] - date1->day;
		if(date1->month <= 2)
			if(leapyear(date1->year))
				diff++;
		for(i=1; i<date2->month; i++)					//date2距离年初多少天
		{
			diff += month[i];
		}
		diff += date2->day;
		if(date1->month > 2)
			if(leapyear(date2->year))
				diff++;
	}

	return diff;
}

int main()
{
	int days = 0;
	DATE day1, day2;
	DATE *date1, *date2;
	date1 = &day1;
	date2 = &day2;
	printf("输入日期：");
	scanf("%d-%d-%d",&(date1->year), &(date1->month), &(date1->day));
	printf("输入另一个日期：");
	scanf("%d-%d-%d",&date2->year, &date2->month, &date2->day);
	compare(date1, date2);
	days = diff(date1, date2);
	printf("两个日期之间共有%d天。\n",days);
	return 0;
}