UIViewController memory management

Hi I have a very basic issue of memory management with my UIViewController (or any other object that I create); The problem is that in Instruments my Object allocation graph is always rising even though I am calling release on then assigning them nil.

I have 2 UIViewController sub-classes each initializing with a NIB; I add the first ViewController to the main window like [window addSubView:first.view]; Then in my first ViewController nib file I have a Button which loads the second ViewController like :

-(IBAction)loadSecondView{
     if(second!=nil){ //second is set as an iVar and @property (nonatomic, retain)ViewController2* second; 
         [second release];
         second=nil;
     }
     second=[[ViewController2 alloc]initWithNibName:@"开发者_Python百科ViewController2" bundle:nil];
     [self.view addSubView:second.view];

}

In my (second) ViewController2 i have a button with an action method

-(IBAction) removeSecond{

    [self.view removeFromSuperView];
}

Please let me know if the above scheme works in a managed way for memory...? In Instruments It does not show release of any allocation and keeps the bar status graph keeps on rising.

First of all, why use this scheme when second is a property:

if(second!=nil){
     [second release];
     second=nil;
 }
 second=[[ViewController2* second]initWithNibName:@"ViewController2" bundle:nil];

A propery automatically releases it's old value when the setter is used. So this could be rewritten as:

if(self.second == nil) { //Prevents creating a new controller if there already is one.
     self.second = [[[ViewController2 alloc] initWithNibName:@"ViewController2" bundle:nil] autorelease];
}

Also, what's up with [ViewController2* second]? Why is that asterisk there, and what does the class method second do?