Abstract Student class program

Student is an abstract class with pure virtual functions getdata() and display(). Concrete classes Engineering, Science and Medical derive from it and override these functions. A base pointer array is used to call the correct version at run time.

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

class Student {                      // abstract class
protected:
    string name;
    int roll;
public:
    virtual void getdata() = 0;      // pure virtual functions
    virtual void display() = 0;
    virtual ~Student() {}
};

class Engineering : public Student {
    string branch;
public:
    void getdata() {
        cout << "Engineering - name, roll, branch: ";
        cin >> name >> roll >> branch;
    }
    void display() {
        cout << "[Engineering] " << name << ", Roll " << roll
             << ", Branch " << branch << endl;
    }
};

class Science : public Student {
    string subject;
public:
    void getdata() {
        cout << "Science - name, roll, major subject: ";
        cin >> name >> roll >> subject;
    }
    void display() {
        cout << "[Science] " << name << ", Roll " << roll
             << ", Major " << subject << endl;
    }
};

class Medical : public Student {
    string specialization;
public:
    void getdata() {
        cout << "Medical - name, roll, specialization: ";
        cin >> name >> roll >> specialization;
    }
    void display() {
        cout << "[Medical] " << name << ", Roll " << roll
             << ", Specialization " << specialization << endl;
    }
};

int main() {
    Student *s[3];
    s[0] = new Engineering;
    s[1] = new Science;
    s[2] = new Medical;

    for (int i = 0; i < 3; i++) s[i]->getdata();   // run-time binding
    cout << "\nStudent records" << endl;
    for (int i = 0; i < 3; i++) s[i]->display();

    for (int i = 0; i < 3; i++) delete s[i];
    return 0;
}

Sample run:

Engineering - name, roll, branch: Ram 1 Computer
Science - name, roll, major subject: Sita 2 Physics
Medical - name, roll, specialization: Hari 3 Surgery

Student records
[Engineering] Ram, Roll 1, Branch Computer
[Science] Sita, Roll 2, Major Physics
[Medical] Hari, Roll 3, Specialization Surgery

new Student is not allowed because the class is abstract. The virtual functions make s[i]->display() call the version of the actual object. The virtual destructor ensures correct clean-up through base pointers.