// number of day in month
NSCalendar* cal = [NSCalendar currentCalendar];
NSDateComponents* comps = [[[NSDateComponents alloc] init] autorelease];
[comps setMonth:[[monthFormat stringFromDate:[NSDate date]] intValue]];
NSRange range = [cal rangeOfUnit:NSDayCalendarUnit
		         inUnit:NSMonthCalendarUnit
			 forDate:[cal dateFromComponents:comps]];

Number of days in a month

iphone

Objective C