Re: Error while writing State Design Pattern Code

Hi All

i am getting Error while writing following code for state design
Pattern
kindly let me know How to Correct this Error ??

Thanks
Pallav Singh

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#include<iostream.h>
using namespace std;

class state;

class Machine
{
class state * current;
public :
Machine();

void setcurrentstate(state * s)
  { current = s ; }

void on();
void off();
};

class state
{
  public :
  virtual void on(Machine * m)
    {cout<< " Already On \n"; }

  virtual void off(Machine * m)
    {cout<<"Already Off \n"; }
};

void Machine::on()
  { current->on(this); }

void Machine::off()
  { current->off(this); }

class ON : public state
{
  public :
  ON() {cout<<"Destructor invoked \n ";}
 ~ON() {cout<<"Constructor invoked \n ";}
  void off(Machine * m);
};

class OFF : public state
{
  public :
  OFF() {cout<<"Destructor invoked \n ";}
 ~OFF() {cout<<"Constructor invoked \n ";}
  void on(Machine * m)
   {cout<<"Going from OFF to ON";
    m->setcurrentstate( new ON() );
    delete this;
   }
};

Machine::Machine()
  {
    current = new OFF();
    cout<<"Machine constructor Called "<<endl;
  }

void ON::off(Machine * m)
  {
    cout<<"Going from ON to OFF";
    m->setcurrentstate( new OFF() );
    delete this;
  }

int main()
{

void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error
Point
 Machine FSM;
 int num;
 while(1)
  { cout <<"Enter 0 / 1 : ";
    cin >> num;
    (FSM.*ptrs[num])();
  }

  return 0;
}

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