iOS Build a Simple iPhone App with Objective-C Creating a Data Model Creating a Data Collection

why we are writing self.shoppingList but not self.shoppingCart in .m file.Also,why no alloc for shoppingCart?

treehouse first App challenge test 3

ViewController.h
#import "UIViewController.h"

@interface ViewController : UIViewController

@property (strong, nonatomic) NSString *shoppingCart;

@property (strong,nonatomic) NSArray *shoppingList;
@end
ViewController.m
#import "ViewController.h"

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
self.shoppingList=[[NSArray alloc] initWithObjects:@"toothpaste",@"bread",@"eggs",nil];
  shoppingCart= [shoppingList objectAtIndex: 2];
    // Add your code below!
}

@end