How to write a modal view

modalview.m

    UIViewController* avc = [[UIViewController alloc] init];
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(50,50,100,100)];
    view.backgroundColor = [UIColor redColor];
    [avc.view addSubview:view];
	
    UIWindow* ow = [[UIWindow alloc] initWithFrame: [UIScreen mainScreen].bounds];
    ow.windowLevel = UIWindowLevelAlert;
    ow.backgroundColor = [UIColor clearColor];
    ow.rootViewController = avc;
    [ow makeKeyAndVisible];