Protected specifier; student/test/result program

Protected access specifier

A member declared protected is accessible within its own class and in classes derived from it, but not from outside code (e.g. main()). It lies between private (only the class) and public (everyone). It lets derived classes use base data while still hiding it from the outside.

Program: multilevel inheritance Student -> Test -> Result

• Student stores roll number and name.
• Test (derived from Student) stores marks in three subjects.
• Result (derived from Test) calculates total and percentage and displays the result.

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

class Student {
protected:
    int roll;
    string name;
public:
    void getInfo() {
        cout << "Enter roll number and name: ";
        cin >> roll >> name;
    }
};

class Test : public Student {
protected:
    float m1, m2, m3;
public:
    void getMarks() {
        cout << "Enter marks in 3 subjects: ";
        cin >> m1 >> m2 >> m3;
    }
};

class Result : public Test {
    float total, percent;
public:
    void calculate() {
        total = m1 + m2 + m3;
        percent = total / 3;
    }
    void display() {
        cout << "\nRoll: " << roll << "  Name: " << name << endl;
        cout << "Marks: " << m1 << ", " << m2 << ", " << m3 << endl;
        cout << "Total = " << total << ", Percentage = " << percent << "%" << endl;
        if (m1 >= 40 && m2 >= 40 && m3 >= 40)
            cout << "Result: Pass" << endl;
        else
            cout << "Result: Fail" << endl;
    }
};

int main() {
    Result r;
    r.getInfo();
    r.getMarks();
    r.calculate();
    r.display();
    return 0;
}

Sample run:

Enter roll number and name: 7 Sita
Enter marks in 3 subjects: 78 65 82

Roll: 7  Name: Sita
Marks: 78, 65, 82
Total = 225, Percentage = 75%
Result: Pass

Result reads roll, name, m1, m2 and m3 directly because they are protected in their parent classes.