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In C++ we can derive a class from a previously defined one.
For example we might need Circle, SquareandTriangle
objects which can be derived from some general class
called Shape.If every shape has in common a colour and an
x-y position, and if every shape can change its position and
colour, then we could start with:
class Shape {
public:
void change_colour (int new_colour);
void move (int x_change, int y_change);
......
private:
int x, y;// coordinates of the origin
int colour;// current colour
.....
};
Shapeis said to be the base class, while Circle, Square
and Triangleare derived classes. The aim here is to make
it possible to re-use code on a grand scale.
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