gistfile1.m

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *thisDayComponents = [[NSDateComponents alloc] init];
[thisDayComponents setYear:2010];
[thisDayComponents setMonth:9];
[thisDayComponents setDay:1];
[thisDayComponents setCalendar:gregorian];

NSString *aDate = [[gregorian dateFromComponents:thisDayComponents] descriptionWithLocale:nil];
NSLog(@"day:%i  date:%@", [thisDayComponents day], aDate);
    
// result => day:1  date:2010-09-01 00:00:00 +0200