1.#include<stdio.h>

int main()
{
int year =1000;
int k = 0;
while ((year >= 1000) && (year < 1999))
{
if ((year % 400 == 0) ||
((year % 100 != 0) && (year % 4 == 0)))
{
printf("%d是闰年\t", year);//t是制表符
k++;
if (k % 3 == 0)
printf("\n");
}
year = year++;
}


return(0);
}

2.#include<stdio.h>
int main()
{
int month, days , year, a;
scanf_s("%d ", &year);
scanf_s("%d ", &month);


if ((year % 400 == 0) ||((year % 4 == 0) && (year % 100 != 0)))
a = 0;
else
a = 1;
switch (month)//开关分支语句
{
case 1:case 3:case 5:case 7:case 8:case 10:case 12:days = 31;

break;//用来跳出
case 4:case 6:case 9:case 11:days = 30;
break;
case 2:
if (a == 1) days = 28;
else days = 29;
break;
default://相当于else
printf("data error");
break;
printf("天数为：%d", days);
}

return 0;
}