How Can I Launch The Appstore App Directly from my Application

- (IBAction)gotoReviews:(id)sender
{
    NSString *str = @"itms-apps://ax.itunes.apple.com/WebObjects/MZStore.woa";
    str = [NSString stringWithFormat:@"%@/wa/viewContentsUserReviews?", str];
    str = [NSString stringWithFormat:@"%@type=Purple+Software&id=", str];

    // Here is the app id from itunesconnect
    str = [NSString stringWithFormat:@"%@289382458", str];

    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:str]];
}

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"itms://itunes.com/apps/appname"]];

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"itms://itunes.com/apps/developername"]];