判断闰年

能被4整除但不能被100整除或者能被400整除

#import <Foundation/Foundation.h>
int main(int agrc, const char * argv[]) {
  @autoerleasepool {
    int year = 2100;
    if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
        NSLog (@"%i is a leap year", year);
    } else {
        NSLog (@"%i is not a leap year", year);
    }
  }
  return 0;
}