C语言练习-计算两个日期间隔

1月1日到1月2日算间隔1天

#include <stdio.h>
int daynumber(int year,int mon,int day)//返回日期在当年是第几天
{
	int a[]={31,28,31,30,31,30,31,31,30,31,30,31};//12个月各多少天
	int i,total=0;
	for(i=0; i<mon-1; i++)//先算当月前有多少天
		total+=a[i];
	if(mon>2) //闰年的2月多一天 算闰年不能放到for里面
		total+=(year%4==0&&year%100!=0 || year%400==0);
	total+=day;//最后加上当月天数
	return total;
}

int yearnumber(int year1,int year2)//返回year1到year2-1 有多少天
{
	int total=0,year;
	for(year=year1; year<year2; year++)
		total+=365+(year%4==0&&year%100!=0 || year%400==0);//year是闰年则多一天
	return total;
}

int main()
{
	int year1,mon1,day1,year2,mon2,day2;
	int dist;//距离
	printf("请输入起始日期 年月日之间用空格隔开\n例如：2019 01 01 2020 12 31\n");
	while(fflush(stdin),//默认year1<year2
	 scanf("%d%d%d%d%d%d",&year1,&mon1,&day1,&year2,&mon2,&day2)!=EOF)
	{
		if(year1==year2)//同一年下
			dist=daynumber(year2,mon2,day2)-daynumber(year1,mon1,day1);
		else
			dist=yearnumber(year1,year2)-daynumber(year1,mon1,day1)
				+daynumber(year2,mon2,day2);
		printf("%04d-%02d-%02d和%04d-%02d-%02d相差%d天\n",
				year1,mon1,day1, year2,mon2,day2, dist);
	}
	return 0;
}