How to compare date string with current date

- (NSString *)dateDifferenceStringFromString:(NSString *)dateString withFormat:(NSString *)dateFormat;
{

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
[dateFormatter setDateFormat:dateFormat];
NSDate *date = [dateFormatter dateFromString:dateString];
[dateFormatter release];
NSDate *now = [NSDate date];
double time = [date timeIntervalSinceDate:now];
time *= -1;
if(time < 1) {
return dateString;
} else if (time < 60) {
return @"less than a minute ago";
} else if (time < 3600) {
int diff = round(time / 60);
if (diff == 1)
return [NSString stringWithFormat:@"1 minute ago", diff];
return [NSString stringWithFormat:@"%d minutes ago", diff];
} else if (time < 86400) {
int diff = round(time / 60 / 60);
if (diff == 1)
return [NSString stringWithFormat:@"1 hour ago", diff];
return [NSString stringWithFormat:@"%d hours ago", diff];
} else if (time < 604800) {
int diff = round(time / 60 / 60 / 24);
if (diff == 1)
return [NSString stringWithFormat:@"yesterday", diff];
if (diff == 7)
return [NSString stringWithFormat:@"last week", diff];
return[NSString stringWithFormat:@"%d days ago", diff];
} else {
int diff = round(time / 60 / 60 / 24 / 7);
if (diff == 1)
return [NSString stringWithFormat:@"last week", diff];
return [NSString stringWithFormat:@"%d weeks ago", diff];
}
}