Queue Implementation with Inheritance and Polymorphism

Following is the source code of simple queue implementation with the help of Inheritance and Polymorphism i.e. Late Binding.

In inheritance, a class (derived class) inherits the features i.e. methods and properties from the parent class (base class). Polymorphism occurs when multiple classes are inherited from each other. Here call to a member function (of the class) causes a different function to be executed (from the classes linked via inheritance) depending on the type of object that invokes the function.

queue implementation C++

#include <dos.h>
#include <stdlib.h>
#include <iostream.h>
#include <conio.h>
#include <windows.h>

#define MAX 5  // MAXIMUM CONTENTS IN QUEUE

class task {
 public:
  virtual void dotask() {}
  task() {}
  int exists;
};

class notep : public task {
 public:
  notep() { exists = 1; }

  void dotask() { system("notepad"); }
};

class regt : public task {
 public:
  regt() { exists = 1; }

  void dotask() { system("regedit"); }
};

class winex : public task {
 public:
  winex() { exists = 1; }

  void dotask() { system("explorer"); }
};

class Bep : public task {
 public:
  Bep() { exists = 1; }

  void dotask() { cout << "\a"; }
};

class MsBox : public task {
 private:
  char* text;
  char* caption;
  int style;

 public:
  MsBox(char* ext, char* cap, int no) {
    text = ext;
    caption = cap;
    exists = 1;
    style = no;
  }

  void dotask() { MessageBox(0, text, caption, style); }
};

class queue {
 private:
  task* t[MAX];
  int al;
  int dl;

 public:
  int opt, opt1, a;
  char te[255], capt[40];

  queue() {
    dl = -1;
    al = -1;
  }

  void del() {
    task* tmp;
    if (dl == -1) {
      cout << "Queue is Empty";
      sleep(2);
    } else {
      t[dl]->exists = 0;
      for (int j = 0; j <= al; j++) {
        if ((j + 1) <= al) {
          tmp = t[j + 1];
          t[j] = tmp;
        } else {
          t[al]->exists = 0;
          al--;

          if (al == -1)
            dl = -1;
          else
            dl = 0;
        }
      }
    }
  }

  void menu() {
    clrscr();
    cout << "1) Add Task \n2)Execute Tasks\n3)Exit Program\n";
    // int opt;
    cin >> opt;
    switch (opt) {
      case 1:
        clrscr();
        cout << "1) Open Notepad\n";
        cout << "2) Open Explorer\n"
             << "3) Open Registry\n"
             << "4) Sound a Beep\n"
             << "5) MessageBox API\n"
             << "6) Back\n";

        cin >> opt1;
        if (opt1 != 6)
          add(opt1);
        break;

      case 2:
        if (al != -1 && dl != -1) {
          for (int k = 0; k <= al; k++) {
            if (t[k]->exists == 1)
              t[k]->dotask();
            t[k]->exists = 0;
          }
          al = dl = -1;
        } else {
          cout << "Queue is Empty";
          sleep(3);
        }
        break;

      case 3:
        exit(0);
        break;
    }
  }

  void add(int item) {
    if (dl == -1 && al == -1) {
      dl++;
      al++;
    } else {
      al++;
      if (al < max) {
      } else {
        cout << "Queue is Full\n";
        al--;
        sleep(3);
        return;
      }
    }
    switch (item) {
      case 1:
        t[al] = new notep;
        break;

      case 2:
        t[al] = new winex;
        break;

      case 3:
        t[al] = new regt;
        break;

      case 4:
        t[al] = new Bep;
        break;

      case 5:
        cout << "\n Enter Style Number:";
        cin >> a;
        t[al] = new MsBox("Task Performed.", "Queue Implementation", a);
        break;

      default:
        cout << "Programming Error";  // No Possibility of this executing
    };
  }
};

void main() {
  queue a;
  while (1) {
    a.menu();
  }
}