C++ Program on Abstract Class Example

   #include <iostream> 

   using namespace std;
   // Base class
   class Shape
   {
     public:
       // pure virtual function providing interface framework.
       virtual int getArea() = 0;
       void setWidth(int w)
       {
         width = w;
       }
       void setHeight(int h)
       {
         height = h;
       }
     protected:
       int width;
       int height;
   };
   // Derived classes
   class Rectangle: public Shape
   {
     public:
       int getArea()
       {
         return (width * height);
       }
   };
   class Triangle: public Shape
   {
     public:
       int getArea()
       {
         return (width * height)/2;
       }
   };
   int main(void)
   {
     Rectangle Rect;
     Triangle Tri;
     Rect.setWidth(5);
     Rect.setHeight(7);
     // Print the area of the object.
     cout << "Total Rectangle area: " << Rect.getArea() << endl;
     Tri.setWidth(5);
     Tri.setHeight(7);
     // Print the area of the object.
     cout << "Total Triangle area: " << Tri.getArea() << endl;
     return 0;
   }