A class can be DERIVED from another class


The new class INHERITS the variables and methods of the BASE CLASS. Additional variables and/or methods can be added: 

#include <iostream.h>
#include <math.h>

class vector
{
public:

double x;
double y;

vector (double a = 0, double b = 0)
{
x = a;
y = b;
}

double module()
{
return sqrt (x*x + y*y);
}

double surface()
{
return x * y;
}
};

class trivector: public vector // trivector is derived from vector
{
public:
double z; // added to x and y from vector

trivector (double m=0, double n=0, double p=0): vector (m, n)
{
z = p; // Vector constructor will
} // be called before trivector
// constructor, with parameters
// m and n.

trivector (vector a) // What to do if a vector is
{ // cast to a trivector
x = a.x;
y = a.y;
z = 0;
}

double module () // define module() for trivector
{
return sqrt (x*x + y*y + z*z);
}

double volume ()
{
return this->surface() * z; // or x * y * z
}
};

void main()
{
vector a (4, 5);
trivector b (1, 2, 3);

cout << "a (4, 5) b (1, 2, 3) *r = b" << endl << endl;

cout << "Surface of a: " << a.surface() << endl;
cout << "Volume of b: " << b.volume() << endl;
cout << "Surface of base of b: " << b.surface() << endl;

cout << "Module of a: " << a.module() << endl;
cout << "Module of b: " << b.module() << endl;
cout << "Module of base of b: " << b.vector::module() << endl;

trivector k;
k = a; // thanks to trivector(vector) definition
// copy of x and y, k.z = 0
vector j;
j = b; // copy of x and y. b.z leaved out

vector *r;
r = &b;

cout << "Surface of r: " << r->surface() << endl;
cout << "Module of r: " << r->module() << endl;
}




Added on May 31, 2007 Comment
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