!(year%4) && year%100 || !(year%400)
求出來的就是閏年!
void main(void){
int year,i,n;
for(n=0,i=2000;i<3000;i+=4)
if(!(year%4) && year%100 || !(year%400)) n++;
printf("In the 21st century, there are %d leap years.\n",n);
}