Demonstrate virtual functons: list interface : List « Data Structure « C++

1. C++
2. Data Structure
3. List

Demonstrate virtual functons: list interface

#include <iostream>
#include <cstdlib>
#include <cctype>
using namespace std;

class list {
public:
  list *head;             // pointer to start of list
  list *tail;             // pointer to end of list 
  list *next;             // pointer to next item
  int num;                // value to be stored

  list() { 
     head = tail = next = NULL; 
  }
  virtual void store(int i) = 0;
  virtual int retrieve() = 0;
};

class queue : public list {
public:
  void store(int i);
  int retrieve();
};

void queue::store(int i)
{
  list *item;

  item = new queue;
  if(!item) {
    cout << "Allocation error.\n";
    exit(1);
  }
  item->num = i;

  if(tail) 
     tail->next = item;
  tail = item;
  item->next = NULL;
  if(!head) 
     head = tail;
}

int queue::retrieve()
{
  int i;
  list *p;

  if(!head) {
    cout << "List empty.\n";
    return 0;
  }

  // remove from start of list
  i = head->num;
  p = head;
  head = head->next;
  delete p;

  return i;
}

class stack : public list {
public:
  void store(int i);
  int retrieve();
};

void stack::store(int i)
{
  list *item;

  item = new stack;
  if(!item) {
    cout << "Allocation error.\n";
    exit(1);
  }
  item->num = i;

  if(head) 
     item->next = head;
  head = item;
  if(!tail) 
     tail = head;
}

int stack::retrieve()
{
  int i;
  list *p;

  if(!head) {
    cout << "List empty.\n";
    return 0;
  }

  // remove from start of list
  i = head->num;
  p = head;
  head = head->next;
  delete p;

  return i;
}

int main()
{
  list *p;

  // demonstrate queue
  queue queueObject;
  p = &queueObject; // point to queue

  p->store(1);
  p->store(2);
  p->store(3);

  cout << "Queue: ";
  cout << p->retrieve();
  cout << p->retrieve();
  cout << p->retrieve();

  cout << '\n';

  // demonstrate stack
  stack stackObject;
  p = &stackObject; // point to stack

  p->store(1);
  p->store(2);
  p->store(3);

  cout << "Stack: ";
  cout << p->retrieve();
  cout << p->retrieve();
  cout << p->retrieve();

  cout << '\n';

  return 0;
}



           
       

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