#include <iostream>

using namespace std;

class Book
{
public:
    string getContents()
    {
        return "Long time ago,There is a temple in the mountain";
    }
};

class Paper
{
public:
    string getContents()
    {
        return "I am handsome";
    }
};

class Mother
{
public:
    
 
void tellstory(Book* b)
    {
        cout << b->getContents() << endl;
    }
    void tellstory(Paper* p)
    {
        cout << p->getContents() << endl;
    }
};

int main(int argc, char *argv[])
{
    Book b;
    Mother m;
    Paper p;
    m.tellstory(&b);
    m.tellstory(
 
&p);
    return 0;
}

#include <iostream>

using namespace std;
class iReader
{
public:
    virtual string getContents() = 0;//only provide a interface
};
class Book : public iReader
{
public:
    string getContents()
    {
        return "Long time ago,There is a temple in the mountain";
    }
};

class Paper : public iReader
{
public:
    string getContents()
    {
        return "I am handsome";
    }
};

class Mother
{
public:
    void tellstory(iReader * r)
    {
        cout << r->getContents() << endl;
    }
};

int main(int argc, char *argv[])
{
    Book b;
    Mother m;
    Paper p;
    m.tellstory(&b);
    m.tellstory(&p);
    return 0;
}

Open closed principle