计算今天是周几

```

NSCalendar *cal = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierRepublicOfChina];

NSInteger comp = [cal component:NSCalendarUnitWeekday fromDate:[NSDate date]];

NSLog(@"%ld",comp);

NSDateComponents *comps = [cal components:NSCalendarUnitWeekday fromDate:[NSDate date]];

NSLog(@"%@",comps);

```