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Polymorphism Example 1 - Derive class Two from class One
1. Without virtual function f1.
cswanson@mega (~/summer05) % cat poly0.cpp
// polymorphism example 0
#include <iostream>
using namespace std;
#include <cmath>
// class declaration for the base class One
class One
{
protected:
double num;
public:
One(double n); // constructor
double f1(); // a member function
double f2(); // another member
function
};
// class implementation for base class One
One::One(double n) : num( n ) {} // constructor
double One::f1()
{
return num/2 ; // divide num by 2
}
double One::f2()
{
return pow(f1(),2) ; // square the result of f1()
}
// class definition for the derived class
class Two : public One
{
public:
Two( double n ); // constructor
double f1(); // this redefines
class One's f1()
};
// class implementation for Two
Two::Two( double n ) : One(n) {} // constructor
double Two::f1()
{
return num/3 ; // divide num by 3
}
// driver program
int main()
{
One object_1(12); // object_1 is an object of the base class
Two object_2(12); // object_2 is an object of the derived
class
// call f2() using a base class object call
cout << "The computed value using a base class object call
is "
<< object_1.f2() <<
endl;
// call f2() using a derived class object call
cout << "The computed value using a derived class object call
is "
<< object_2.f2() << endl;
return 0;
}
% g++ poly0.cpp
% a.out
The computed value using a base class object call is 36
The computed value using a derived class object call is 36
<--- INCORRECT
2. With viirtual function f1
cswanson@mega (~/summer05) % cat poly0.cpp
// polymorphism example 0
#include <iostream>
using namespace std;
#include <cmath>
// class declaration for the base class One
class One
{
protected:
double num;
public:
One(double n); // constructor
virtual double f1(); // a
member function
double f2(); // another member
function
};
// class implementation for base class One
One::One(double n) : num( n ) {} // constructor
double One::f1()
{
return num/2 ; // divide num by 2
}
double One::f2()
{
return pow(f1(),2) ; // square the result of f1()
}
// class definition for the derived class
class Two : public One
{
public:
Two( double n ); // constructor
double f1(); // this redefines
class One's f1()
};
// class implementation for Two
Two::Two( double n ) : One(n) {} // constructor
double Two::f1()
{
return num/3 ; // divide num by 3
}
// driver program
int main()
{
One object_1(12); // object_1 is an object of the base class
Two object_2(12); // object_2 is an object of the derived
class
// call f2() using a base class object call
cout << "The computed value using a base class object call
is "
<< object_1.f2() <<
endl;
// call f2() using a derived class object call
cout << "The computed value using a derived class object call
is "
<< object_2.f2() << endl;
return 0;
}
cswanson@mega (~/summer05) % g++ poly0.cpp
cswanson@mega (~/summer05) % a.out
The computed value using a base class object call is 36
The computed value using a derived class object call is 16
<--- CORRECT
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