从键盘输入年份，判断是否是闰年。
#include
int main(void)
{
int year,yes;
scanf("%d",&year);
if(year%4==0&&year%100!=0) yes=1;
else if(    ) yes=1; /*第一空*/
else      ; /*第二空*/
if(    ) printf("%d is ",year); /*第三空*/
else printf("%d is not ",year);
printf("a leap year.\n");
returm 0;
}