inheritence compiling issue

    #include <memory>
    #include <iostream>
    #include <cstdlib>
    #include <string>
    #include <vector>
    
    using namespace std; // io namespace used
    volatile int isopen; // global variable that tells if the park is open
    volatile int inpark; // global variable that tells how many are in the park
    
    // people classes -- workers and visitors
      
    class visitor{ // visitors to park
    private:
      int prk; // are we in the park?
      int exhibit; // how many exhibits have we viewed
      int wlk; // are we walking?
      
    public:
      visitor(): prk(0), exhibit(0), wlk(0){ cout << "\n A zoo visitor arrived."; }; // create the visitor
      void walk(){ wlk++; cout << "\n Walking to an exhibit."; return; }; // walk between exhibits
      void watch(){ exhibit++; cout << "\n Watching an exhibit."; return; }; // keep track of viewed exhibits
      void enter(){ prk++; inpark++; cout << "\n I'm entering the zoo."; return; }; // let user know person entered zoo
      ~visitor(){ cout << "\n I'm leaving the zoo."; }; // let user know person left zoo; destroy thread
    
      void vrun(){ // class that runs the "person" (thread)
    	while (exhibit<3){ //
    	  if(prk){ // we're in the park
    	if(wlk){ wlk--; watch(); return; } // watch some animals
    	else{ walk(); return; } // walk to an exhibit
    	  }else{ enter(); return; }
    	}
 	if(exhibit>=3){ prk--; inpark--; cout << "\n I'm ready to leave the zoo."; return; } // get ready to leave
      };
    };
    
    class staff{ // zoo staff
    public:
      staff(){ cout << "\n A staff member has arrived"; } // initiate staffer
      void cleanPark(){ cout << "\n Staff is cleaning park"; return; }; // enter work mode
      void cleanExhibit(){ cout << "\n Staff is cleaning exhibit"; return; }; // enter work mode
      void feedAnimals(){ cout << "\n Staff is feeding animals"; return; }; // enter work mode
      ~staff(){ cout << "\n Leaving for the night."; }; // deallocate staff
    
      void srun(){ // class that "runs" the staffer
    	while(isopen){ // while the park is open (use global variable)
    	  switch(rand()%3){ // randomly choose what to do
    	  case '0': cleanPark(); break;
    	  case '1': cleanExhibit(); break;
    	  case '2': feedAnimals(); break;
    	  }
    	  return;
    	}
      };
    };
    
    // animal classes -- attractions at the zoo
    
    class animal{ // main animal class
    protected:
      const string antype; // animal type
    
    public:
      animal(){}; // overloaded constructer
      animal(string Antype): antype(Antype){ // animal constructor
    	cout << "\n A(n) " << antype << " is restless."; }; // creates animal
      void eat(){ cout << "\n this " << antype << " eating."; return; }; // doing something 
      void sleep(){ cout << "\n this " << antype << " sleeping."; return; }; // doing something 
      void play(){ cout << "\n this " << antype << " playing."; return; }; // doing something 
      ~animal(){ cout << "\n " << antype << " is resting.";}; // destructor
    
      void run(){ // function that runs the "animal"
    	while(isopen){ // while the park is open.... (use global variable)
    	  switch(rand()%3){ // randomly choose what to do
    	  case '0': eat(); break;
    	  case '1': sleep(); break;
    	  case '2': play(); break;
    	  }
    	}
      };
    };
    
    class lion: public animal { // lions
    public:
      lion(): animal("lion"){}; // let user know lion is here
    };
    /*
    class dolphin: public animal{ // dolphins
    public:
      dolphin(): animal("dolphin"){}; // let user know dolphin is here 
    };
    
    class monkey: public animal{ // monkeys
    public:
      monkey(): animal("monkey"){}; // let user know monkey is here
    };
    
    class bird: public animal{ // birds
    public:
      bird(): animal("bird"){}; // let user know bird is here
    };
    */
    // main zoo class
    
    int main(){ // main class and actual prgram
      // main class interacts with user; determines how much of each thing to make (user input)
    
      // planned changes after getting threads working: add arrays for feeding each type of animal
      // and cleaning each exhibit.  add variable to expand upon animal activities: dolphin shows, etc.
    
      int amtvis,amtstaff,amtl,amtd,amtm,amtb; // numbers to be retrieved from user
      inpark=0; // use global variable? how many in park?
      isopen=1; // use global variable? park is open
      int i,j; // for-loop counter/switch switch
    
      cout << "\n How many people plan to visit the zoo today?\n"; // ask user for number of visitors
      cin >> amtvis; // get number of visitors from user
 cout << " How many people does the zoo have on staff today?\n"; // get staff; may limit other things in add ons to the program
      cin >> amtstaff; // get number of staffers from user
      cout << " How many lions does the zoo have?\n"; // how many lions
      cin >> amtl; // get number of lions
    /*  cout << " How many dolphins does the zoo have?\n"; // how many dolphins
      cin >> amtd; // get number of dolphins
      cout << " How many monkeys does the zoo have?\n"; // how many monkeys
      cin >> amtm; // get number of monkeys
      cout << " How many birds does the zoo have?\n"; // how many birds
      cin >> amtb; // get number of birds
    */
      vector<lion*> lions(amtl);
    /* vector<dolphin*> dolphins(amtd); vector<monkey*> monkeys(amtm); // animals
      vector<bird*> birds(amtb); // more animals
    */  vector<staff*> staffers(amtstaff); vector<visitor*> visitors(amtvis); // people
    
      // create animals, staff and visitors; make them do stuff
      for(i=0;i<amtl;i++){ lions[i] = new lion(); } // create each lion
    /*  for(i=0;i<amtd;i++){ dolphins[i] = new dolphin(); } // create each dolphin
      for(i=0;i<amtm;i++){ monkeys[i] = new monkey(); } // create each monkey
      for(i=0;i<amtb;i++){ birds[i] = new bird(); } // create each bird
    */  for(i=0;i<amtstaff;i++){ staffers[i] = new staff(); } // create each staff
      for(i=0;i<amtvis;i++){ visitors[i] = new visitor(); } // create each visitor
    
      cout << "\n The zoo is now open."; // open the park
      visitors[(rand()%amtvis)] -> enter(); // send in the first visitor
    
      while(inpark>0){ // random sayings from park management over a loudspeaker while park is open
    	switch(rand()%3){ // randomly choose which type to send into action
    	case 0: visitors[(rand()%amtvis)] -> vrun(); break; // make a visitor do stuff
    	case 1: staffers[(rand()%amtstaff)] -> srun(); break; // make a staffer do something
 	case 2: cout << "debug::lion"; lions[(rand()%amtl)] -> run(); break; // make a lion do something
 /*	case 3: cout << "debug::dolphin"; dolphins[(rand()%amtd)] -> run(); break; // make a dolphin do something
 	case 4: cout << "debug::monkey"; monkeys[(rand()%amtm)] -> run(); break; // make a monkey do something
 	case 5: cout << "debug::bird"; birds[(rand()%amtb)] -> run(); break; // make a bird do something
    */	}
      }
    
      isopen=0; // close the park (end animal and staff threads)
      for(i=0;i<amtvis;i++){ delete visitors[i]; } // remove the visitors
      for(i=0;i<amtstaff;i++){ delete staffers[i]; } // deallocate the staff
      for(i=0;i<amtl;i++){ delete lions[i]; } // deallocate lions
    /*  for(i=0;i<amtd;i++){ delete dolphins[i]; } // deallocate dolphins
      for(i=0;i<amtb;i++){ delete birds[i]; } // deallocate birds
      for(i=0;i<amtm;i++){ delete monkeys[i]; } // deallocate monkeys
    */
      cout << "\n Zoo simulation has ended. \n"; // let user know simulation is over
      return 0; // successful exit
    };