State Design Pattern code in C++

State Design Pattern to design a Music System in C++ language.
#include<iostream>
using namespace std;

//current_context class
class State;
class MusicSystem
{
private:
    State *currentState;
public:
    MusicSystem();

    void stopMusic();
    void playMusic();
    void playNextTrack();
    void playPreviousTrack();
    void setCurrentContext(State* s)
    {
    currentState=s;
    }
};

//abstract state class

class State
{
public:
    virtual void offState(MusicSystem *ms){cout<<"Already Stopped"<<endl;}
    virtual void onState(MusicSystem* ms){cout<<"Already Playing"<<endl;}
    virtual void playNextTrack(MusicSystem* ms){cout<<"Can not play Next in off state."<<endl;}
    virtual void playPreviousTrack(MusicSystem* ms){cout<<"Can not play Previous in off state."<<endl;}
};
//concrete state class on
class OFF:public State
{
public:
    void onState(MusicSystem *ms);
};

//concrete state class off
class ON:public State
{
public:
    void offState(MusicSystem *ms);
    void playNextTrack(MusicSystem *ms);
    void playPreviousTrack(MusicSystem *ms);
};

MusicSystem::MusicSystem()
{
    currentState=new OFF;
}
void MusicSystem::stopMusic()
{
    currentState->offState(this);   
}
void MusicSystem::playMusic()
{
    currentState->onState(this);   
}
void MusicSystem::playNextTrack()
{
    currentState->playNextTrack(this);   
}
void MusicSystem::playPreviousTrack()
{
    currentState->playPreviousTrack(this);   
}


    void OFF::onState(MusicSystem *ms)
    {
    cout<<"Turning from stopped to Play."<<endl;
    ms->setCurrentContext(new ON());
    delete this;
    }
    void ON::offState(MusicSystem *ms)
    {
    cout<<"Turning from Playing to Stopped."<<endl;
    ms->setCurrentContext(new OFF());
    delete this;
    }
    void ON::playNextTrack(MusicSystem *ms)
    {
    cout<<"Playing next track..."<<endl;
    //ms->setCurrentContext(new OFF());
    //delete this;
    }
    void ON::playPreviousTrack(MusicSystem *ms)
    {
    cout<<"Playing previous track..."<<endl;
    //ms->setCurrentContext(new OFF());
    //delete this;
    }


//main
int main()
{
MusicSystem ms;

ms.MusicSystem::stopMusic();
ms.MusicSystem::stopMusic();
ms.MusicSystem::stopMusic();
ms.MusicSystem::playNextTrack();
ms.MusicSystem::playPreviousTrack();

ms.MusicSystem::playMusic();
ms.MusicSystem::playMusic();
ms.MusicSystem::playMusic();
ms.MusicSystem::playNextTrack();
ms.MusicSystem::playPreviousTrack();

ms.MusicSystem::stopMusic();
ms.MusicSystem::playNextTrack();
ms.MusicSystem::playPreviousTrack();

return 0;
}