array of objects

[jdforlife]

I have a the following classes:
parent classed called "CPolygon"
and its child class called "CTriangle" and "CRectangle"

In the main function how do I create an ARRAY of class 'CPolygon' dynamically and when the user says he wants to create a new Triangle, the CPoly[i] will become a new Triangle object and so goes for creating a Rectangle object.
I cannot use vector for this.
I read the documentation file and other forums.

Thanks in advance.

#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area (void) =0;
    void printarea (void)
      { cout << this->area() << endl; }
  };

class CRectangle: public CPolygon {
  public:
    int area (void)
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area (void)
      { return (width * height / 2); }
  };

int main () {
  
  //create an array of CPolygon objects called OPoly[] that will be dynamically 
  //increased as the user enters new entries

  int choice;
  while(1){
  cout<< "1: Trianlge\n2: Rectangle"<<endl;
  cin<<choice;

  if(choice==1)
  {
     //make this object of CPolygon array, an object of CTriangle
     //do some work here related to CTraingle
  }
  else
  {
     //make this object of CPolygon array, an object of CRectangle
     //do some work here related to CRectangle
  }
  //increase array OPoly here
  }
}

[tath]

CPolygon *p can point to all children classes, so in this case:

p = new CRectangle();
or
p = new CTriangle();

For array which you want just create array of CPolygon pointers:

int size;
cin >> size;
CPolygon  **p;

p = new CPolygon *[size];
and now fill the array however you want:

p[0] = new CRectangle();
p[1] = new CTriangle();

and use like:
p[0]->set_values (2,2);

and obviously dont forget to clean the memory after you are done

[jdforlife]

Thank you so much tath!!
But still, one problem remains unsolved for me... How to increase the array size dynamically without "cin>>size"... like everytime the it comes to the end of the while loop in my previous code, can't I increase the size of the array by 1 so that another CPolygon can be made... without using vectors

Thanks again.

[mutexe]

surely this doesnt require the use of maloc or realloc??

[tath]

You can also create simple Linked List class.

[jdforlife]

I saw a method of the object array being copied to another array of objects with one object more, then the previous one getting deleted.
Is this also correct?

Thank you tath

[jdforlife]

Thank you all, specially tath for answering my query.
I have finally finished the program I wanted thanks to you all :)

[tath]

No problem :). Just select this topic as Solved.