Remove all settings from viewcontroller when dismissed - objective-c

Question

I got multiple viewcontrollers in my project. The first viewcontroller is called when the application starts and it presents a login screen. When the credentials are correct and the user logs in, the modalview is dismissed. and another viewcontroller is instantiated like this:
[self dismissModalViewControllerAnimated:NO];
Form *formcontroller = [[Form alloc] init];
[self presentModalViewController:formcontroller animated:YES];
When my other viewcontroller is presented the old one disappears. On the top of my secondviewcontroller i got an logout button, wich does exactly the same, so it dismisses the current viewcontroller and calls another like this:
-(IBAction)logOut:(id)sender{
[self dissmissModalViewControllerAnimated:NO];
}
And in my viewdiddisappear:
-(void)viewDidDisappear:(BOOL)animated{
Postform3ViewController *logincontroller = [[Postform3ViewController alloc] init];
[self presentModalViewController:logincontroller animated:YES];
}
The problem is:
When i push the logout button, and i return back to the logincontroller. The Credentials are still filled in. So my conclusion is that the first viewcontroller stays in memory. What am i doing wrong?
Edit:
I did find my own solution. I was profiling my application, and couldn't find any memory leaks. So i decided everything is released. Then i thought that i was able to set everything to empty myself. I did that in the viewDidAppear method like this:
-(void)viewDidAppear:(BOOL)animated {
gebruikersnaam.text = #"";
wachtwoord.text = #"";
[self.activeTextField resignFirstResponder];
[super viewDidAppear:animated];
}

Answer 1

Well first of all when you are using presentModalViewController and pushViewController the VC is retained so you should always release it after you have presented or pushed it.
Secondly in the third block of code it looks like you are creating a logincontroller but presenting a formcontroller. Perhaps you want to be presenting the VC you had just created:
[self presentModalViewController:logincontroller animated:animated];
Edit 0: For your code, in the first block, release like this:
Form *formcontroller = [[Form alloc] init];
[self presentModalViewController:formcontroller animated:YES];
...
[self dismissModalViewController:formcontroller animated:YES];
[formcontroller release];