initWithString function is not present in NSDate class for iOS Platforms, since you'll need to first specify a date formatter using NSDateFormatter which converts textual representations of dates and times into NSDate objects. Use something like this :
NSString *currentDateString = @"2013-03-24 10:45:32";
NSDateFormatter *dateFormater = [[NSDateFormatter alloc] init];
[dateFormater setDateFormat:@"yyyy-MM-DD HH:mm:ss"];
NSDate *currentDate = [dateFormater dateFromString:currentDateString];
