Show us the code inside of the AppDelegate.cpp file.

#include "AppDelegate.h"
#include "MainMenuScene.h"

USING_NS_CC;

AppDelegate::AppDelegate() {

}

AppDelegate::~AppDelegate()
{
}

//if you want a different context,just modify the value of glContextAttrs
//it will takes effect on all platforms
void AppDelegate::initGLContextAttrs()
{
    //set OpenGL context attributions,now can only set six attributions:
    //red,green,blue,alpha,depth,stencil
    GLContextAttrs glContextAttrs = {8, 8, 8, 8, 24, 8};

    GLView::setGLContextAttrs(glContextAttrs);
}

// If you want to use packages manager to install more packages,
// don't modify or remove this function
static int register_all_packages()
{
    return 0; //flag for packages manager
}

bool AppDelegate::applicationDidFinishLaunching() {
    // initialize director
    auto director = Director::getInstance();
    auto glview = director->getOpenGLView();
    if(!glview) {

        glview = GLViewImpl::create("Game");

        director->setOpenGLView(glview);
    }

    // turn on display FPS
    director->setDisplayStats(true);

    // set FPS. the default value is 1.0/60 if you don't call this
    director->setAnimationInterval(1.0 / 60);
    
    auto fileUtils = FileUtils::getInstance();
    auto screenSize = glview->getFrameSize();
    std::vector<std::string> resDirOrders;
    
    //Check which assets the device requires
    if (2048 == screenSize.width || 2048 == screenSize.height)//retina iPad
    {
        resDirOrders.push_back("ipadhd");
        resDirOrders.push_back("ipad");
        resDirOrders.push_back("iphonehd5");
        resDirOrders.push_back("iphonehd");
        resDirOrders.push_back("iphone");
        
        glview->setDesignResolutionSize(1536, 2048, ResolutionPolicy::NO_BORDER);
    }
    
    else if (1024 == screenSize.width || 1024 == screenSize.height)//no retina ipad
    {
        resDirOrders.push_back("ipad");
        resDirOrders.push_back("iphonehd5");
        resDirOrders.push_back("iphonehd");
        resDirOrders.push_back("iphone");
        
        glview->setDesignResolutionSize(768, 1024, ResolutionPolicy::NO_BORDER);
    }
    else if (1136 == screenSize.width || 1136 == screenSize.height)//retina iphone (5 and 5S)
    {
        resDirOrders.push_back("iphonehd5");
        resDirOrders.push_back("iphonehd");
        resDirOrders.push_back("iphone");
        
        glview->setDesignResolutionSize(640, 1136, ResolutionPolicy::NO_BORDER);
    }
    else if (960 == screenSize.width || 960 == screenSize.height)//retina iphone (4 and 4S)
    {
        resDirOrders.push_back("iphonehd");
        resDirOrders.push_back("iphone");
        
        glview->setDesignResolutionSize(640, 960, ResolutionPolicy::NO_BORDER);
    }
    else //non retina iPhone and Android devices
    {
        if (1080 < screenSize.width) //android devices that have a high resolution
        {
            resDirOrders.push_back("iphonehd");
            resDirOrders.push_back("iphone");
            
            glview->setDesignResolutionSize(640, 960, ResolutionPolicy::NO_BORDER);
        }
        else //non retina iPhone and Android devices with lower resolutions
        {
            resDirOrders.push_back("iphone");
            
            glview->setDesignResolutionSize(320, 480, ResolutionPolicy::NO_BORDER);
        }
    }
    
    fileUtils->setSearchPaths(resDirOrders);
    
    //create a scene. it's an autorelease object
    auto scene = MainMenu::createScene();
    
    //run
    director->runWithScene(scene);

    return true;
}

// This function will be called when the app is inactive. When comes a phone call,it's be invoked too
void AppDelegate::applicationDidEnterBackground() {
    Director::getInstance()->stopAnimation();

    // if you use SimpleAudioEngine, it must be pause
    // SimpleAudioEngine::getInstance()->pauseBackgroundMusic();
}

// this function will be called when the app is active again
void AppDelegate::applicationWillEnterForeground() {
    Director::getInstance()->startAnimation();

    // if you use SimpleAudioEngine, it must resume here
    // SimpleAudioEngine::getInstance()->resumeBackgroundMusic();
}

Have you tried using the source code and project.

What do you mea ?

That was given for the book.