9-1定义一个结构体计算该日是本年中的第几天。

#include
struct  {
	int year;
	int month;
	int day;
}date;
int main(){
	int days;
	printf("输入年月日：\n");
	scanf("%d,%d,%d",&date.year,&date.month,&date.day);
	switch(date.month){
		case 1:days=date.day; break;
		case 2:days=date.day+31; break;
		case 3:days=date.day+59; break;
		case 4:days=date.day+90; break;
		case 5:days=date.day+120; break;
		case 6:days=date.day+151; break;
		case 7:days=date.day+181; break;
		case 8:days=date.day+212; break;
		case 9:days=date.day+243; break;
		case 10:days=date.day+273; break;
		case 11:days=date.day+304; break;
		case 12:days=date.day+334; break;
	}
	if((date.year%4==0&&date.year%100!=0||date.year%400==0)&&date.month>=3){
		days=days+1;
	}
	printf("%d年%d月%d日是%d年的第%d天",date.year,date.month,date.day,date.year,days);
}