右移时，负数补1，正数补0，补符号位；左移补0；移位可以用来取数。位操作时最好不要用（+—*/）  shell  gg=G对齐  command d退出程序作用域： 在复合语句里定义的变量只能在复合语句中使用// 在.m文件中定义的属性、成员变量、以及方法，只能在当前类中访问，不开放出去// 面向对象程序设计的原则：开放封闭原则，开闭原则，对内部开放，对外部封闭#import "AppDelegate.h"#import "FisrtViewController.h"@interface AppDelegate ()            @end@implementation AppDelegate            - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];    // Override point for customization after application launch.    self.window.backgroundColor = [UIColor whiteColor];    [self.window makeKeyAndVisible];        //声明一个视图控制器用于导航器加载    FisrtViewController *fViewController=[[FisrtViewController alloc]init];    fViewController.view.backgroundColor=[UIColor blueColor];    //定义一个导航器来加载第一个视图控制器，即跟视图控制器    UINavigationController *navController=[[UINavigationController alloc]initWithRootViewController:fViewController];    self.window.rootViewController=navController;        return YES;}//第一个视图控制器类的实现文件#import "FisrtViewController.h"#import "SecondViewController.h"@interface FisrtViewController ()@end@implementation FisrtViewController- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];    if (self) {        // Custom initialization    }    return self;}- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view.        //在跟视图控制器中添加一个标签和按钮    UILabel *label=[[UILabel alloc]initWithFrame:CGRectMake(0, 64, 100, 30)];    label.text=@"我是label";    label.textColor=[UIColor redColor];    label.backgroundColor=[UIColor whiteColor];    [self.view addSubview:label];        UIButton *nextBtn=[UIButton buttonWithType:UIButtonTypeCustom];    nextBtn.frame=CGRectMake(220, 64, 100, 30);    [nextBtn setTitle:@"nextView" forState:UIControlStateNormal];    [nextBtn setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];    nextBtn.backgroundColor=[UIColor redColor];    [nextBtn addTarget:self action:@selector(nextDidClik:) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:nextBtn];        UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(30, 144, 240, 296)];    imageView.image=[UIImage imageNamed:@"1.png"];    [self.view addSubview:imageView];}//按钮触发时加载到第二个视图控制器- (void)nextDidClik:(UIButton *)sender{    SecondViewController *secondViewController=[[SecondViewController alloc]init];    secondViewController.view.backgroundColor=[UIColor yellowColor];        [self.navigationController pushViewController:secondViewController animated:YES];    }//第二个视图控制器类的实现文件#import "SecondViewController.h"@interface SecondViewController ()@end@implementation SecondViewController- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];    if (self) {        // Custom initialization    }    return self;}- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view.    UIButton *beforeBtn=[UIButton buttonWithType:UIButtonTypeCustom];    beforeBtn.frame=CGRectMake(0, 64, 100, 30);    [beforeBtn setTitle:@"beforeView" forState:UIControlStateNormal];    [beforeBtn setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];    beforeBtn.backgroundColor=[UIColor redColor];    [beforeBtn addTarget:self action:@selector(beforeBtn:) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:beforeBtn];    }//按钮触发时返回到前一个视图控制器中- (void)beforeBtn:(UIButton *)sender{    [self.navigationController popToRootViewControllerAnimated:YES];}