arc4random_uniform
returns integer value. If you want to implement this, then you might need to use this -
[self.navigationController pushViewController:[controllers objectAtIndex:arc4random_uniform(controllers.count)] animated:YES];
Update -
NSString *className = [controllers objectAtIndex:arc4random_uniform(controllers.count)];
UIViewController *viewController = (UIViewController*)[[NSClassFromString(@"NameofClass") alloc] init];
[self.navigationController pushViewController:viewController animated:YES];