obj c car 未拆分(此程序不符合内存管理规则)

xcode4.2，未拆分程序，都在一个文件内

//
//  main.m
//  carDemo
//
//  Created by Wunderman on 12-1-3.
//  Copyright (c) 2012年 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Tire : NSObject {
    int index;
}
- (int) index;
- (void) setIndex : (int) i;
@end

@implementation Tire

- (int) index {
    return index;  
};
- (void) setIndex : (int) i {
    index = i;
}


- (NSString *) description {
    //return (@"I am a tire. i'am in %d", index);
    NSString* sFormat = [[NSString alloc] initWithFormat: @"I am a tire. i'am in %d", index];
    NSString* string = [[NSString alloc] initWithString: sFormat];
    return string;
}
@end //Tire impl

@interface Engine : NSObject 
@end

@implementation Engine
- (NSString *) description {
    return (@"I am a engine. Vrooom");
}
@end //Engine impl

@interface Car : NSObject {
    Engine *engine;
    Tire *tires[4];
}

//engine's get set
- (Engine *) engine;
- (void) setEngine : (Engine *) newEngine;

//tire's get set
- (Tire *)tireAtIndex: (int) index;
- (void) setTire: (Tire *) tire
         atIndex: (int) index;

- (void) print;
@end //  Car inter

@implementation Car

/*
- (id)init {
    self = [super init];
    if (self) {
        engine = [[Engine alloc] init];
        tires[0] = [[Tire alloc] init];
        tires[1] = [[Tire alloc] init];
        tires[2] = [[Tire alloc] init];
        tires[3] = [[Tire alloc] init];
    }
    return self;
}
*/
- (Engine *) engine {
    return engine;
}

- (void) setEngine:(Engine *) newEngine {
    engine = newEngine;
}

- (Tire *)tireAtIndex: (int) index {
    if (index >3 || index < 0) {
        NSLog(@"bad index %d", index);
        exit(1);
    }
    return tires[index];
}

- (void) setTire: (Tire *) tire
         atIndex: (int) index {
    if (index >3 || index < 0) {
        NSLog(@"bad index %d", index);
        exit(1);
    }
    tires[index] = tire;
}// car impl

- (void) print {
    NSLog(@"%@", engine);
    NSLog(@"%@", tires[0]);
    NSLog(@"%@", tires[1]);
    NSLog(@"%@", tires[2]);
    NSLog(@"%@", tires[3]);
}

@end// Car

int main (int argc, const char * argv[])
{

    @autoreleasepool {
        
        // insert code here...
        NSLog(@"Hello, World!");
        Car *car = [[Car alloc] init];
        
        Engine *engine = [[Engine alloc] init];
        [car setEngine: engine];
        int i;
        for (i=0; i<4; i++) {
            Tire *tire = [[Tire alloc] init];
            [tire setIndex: i];
            [car setTire:tire
                 atIndex:i];
        }
        [car print];
    }
    return 0;
}