C++ Interfaces

class Box
{
   public:
      // pure virtaul function
      virtual double getVolume() = 0;
   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

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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;
}

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Total Rectangle area: 35
Total Triangle area: 17