Turning public into protected

If a class Person is declared and a class Teacher, derived from Person, is declared: 
class Teacher: protected Person{};
The protected keyword ensures that: all public members of Person will be protected in Teacher, all protected members of Person will be protected in Teacher, all private members of Person will be private in Teacher. Basically it upgrades the privacy level of the inherited class members to "at least protected". If the derived class were defined as: 
class Teacher : private Person{};
all public and protected base class members would become private in the derived class. In the following program, the functions setNameAge() and printNameAge() are declared as public in the Person base class. But they are inherited as protected in the derived Teacher class, hence they are unknown outside Teacher. For such a reason, the statements commented out in main(): 
teacher1.setNameAge("Frank", 78);
teacher1.printNameAge();
couldn't compile if included in the code.

Example


#include <iostream>
#include <string>
using namespace std;

class Person

{
     string name;
     int age;
public:
     void setNameAge(string aName, int anAge)
     {
           name = aName;
           age = anAge;
     }

     void printNameAge()
     {
           cout << "name: " << name << " age: " << age << "\n";
     }
};

class Teacher : protected Person // all members of Person
                             // are inherited as protected
{
     string subject;
public:
     void setSubject(string aSubject)
     {
           subject = aSubject;
     }

     void printSubject()  {
           cout << "subject is: " << subject;
     }
};

int main()
{
     Person person1;
     person1.setNameAge("John" , 23);
     Teacher teacher1;
     /*
The following two statements would cause a compilation error
if included in the code. The reason is that all public members
of Person have become protected in Teacher, hence they are not
accessible outside the Teacher class.
   */ 
     //teacher1.setNameAge("Frank", 78);
     //teacher1.printNameAge();
     teacher1.setSubject("Math");
     person1.printNameAge();
     teacher1.printSubject();
}

Output

name: John age: 23
subject is: Math