Simple question - how to create a superclass?

Question

So I've recently started programming, and I'm using a book to learn. It's the 2nd edition of Objective-C for Absolute Beginners.
Anyway, I'm up to the 5th chapter which deals with classes, and one of the tasks at the end of the chapter is to create a superclass.
The example is of a bookstore. Let's say I make a class called PrintedMaterials (this will be the superclass). Now I want to make some (sub)classes called Books, Newpapers and Magazines, the superclass of which will be PrintedMaterials.
How do I go about doing this? I can make Objective-C classes under NSObject, but I don't know how to make them subclasses of another class.
I have Xcode 4.2 and I'm running Mac OS X 10.7.2.
Thanks.

Answer 1

//  PrintedMaterial.h
//  Created by Michael Superczynski on 1/25/12.
//  Copyright 2012 HyperNova Software. All rights reserved.
@interface PrintedMaterial : NSObject
    BOOL available;
@property BOOL available;
@end
//  PrintedMaterial.m
//  Created by Michael Superczynski on 1/25/12.
//  Copyright 2012 HyperNova Software. All rights reserved.
#import "PrintedMaterial.h"
@implementation PrintedMaterial
@synthesize available;
-(id)init
    self = [super init];
    if (self)
        available = YES;
    return self;
//  Book.h
//  Created by Michael Superczynski on 1/25/12.
//  Copyright 2012 HyperNova Software. All rights reserved.
@interface Book : PrintedMaterial
    NSString *title;
@property (nonatomic, strong) NSString *title;
@end
//  Book.m
//  Created by Michael Superczynski on 1/25/12.
//  Copyright 2012 HyperNova Software. All rights reserved.
#import "Book.h"
#import "PrintedMaterial.h"
@implementation Book
@synthesize title;
-(id)init
    self = [super init];
    if (self)
        title = @"Learning Objective-C";
    return self;
-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    PrintedMaterial *thePrintedMaterial  = [[PrintedMaterial alloc] init];
    Book *book = [[Book alloc]init];
    self.book.title = "Learning Xcode";