Pure virtual function called in abstract classes (c++ polymorphism)

program-ape › Uncategorized
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I learned that pure virtual function can be called in abstract classes.
Let’s look at an example:

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#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 () {
  CRectangle rectangle;
  CTriangle triangle;
  CPolygon * ppoly1 = &rectangle;
  CPolygon * ppoly2 = &triangle;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly1->printarea();
  ppoly2->printarea();
  return 0;
}

The output will be:

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20
10

Reference:
Polymorphism