Object Oriented Programming (OOP) using C++ - Lecture 3

Introduction to Object Oriented Programming (OOP) using C++ Programming Language, covering the very basics for newcomers.

1. Object Oriented
Programming using C++
By Mohamed Gamal
© Mohamed Gamal 2024

2. The topics of today’s lecture:
Agenda

4. #include <iostream>
#include <string>
using namespace std;
class Car {
private:
string make;
double price;
int year;
public:
Car() : make(""), price(0.0), year(0)
{ }
Car(string carMake, double carPrice, int carYear)
{
make = carMake;
price = carPrice;
year = carYear;
}
void setDetails() {
cout << "Enter car make: ";
getline(cin, make);
cout << "Enter car price: ";
cin >> price;
cout << "Enter production year: " ;
cin >> year;
}
void displayDetails() const {
cout << "Car Make (Company): " << make << endl;
cout << "Car Price: " << price << endl;
cout << "Car Year: " << year << endl;
}
};
int main() {
Car myCar;
// Get car details
myCar.setDetails();
// Show the car details
cout << "Car Details:\n";
myCar.displayDetails();
return 0;
}
Example
Car Class

6. Inheritance in OOP
–Inheritance is probably the most powerful feature of object-oriented
programming, after classes themselves.
–Inheritance is the process of creating new classes, called derived classes, from
existing or base classes.
–The derived class inherits all the capabilities of the base class but can add
embellishments and refinements of its own.
–The main class remain unchanged.
–Inheritance allows code reusability.

8. #include <iostream>
using namespace std;
class Counter //base class
{
protected: //NOTE: not private
unsigned int count; //count
public:
Counter() : count(0) //no-arg constructor
{ }
Counter(int c) : count(c) //1-arg constructor
{ }
unsigned int get_count() const //return count
{
return count;
}
Counter operator ++ () //incr count (prefix)
{
return Counter(++count);
}
};
class CountDn : public Counter //derived class
{
public:
Counter operator -- () //decr count (prefix)
{
return Counter(--count);
}
};
int main()
{
CountDn c1; //c1 of class CountDn
cout << "c1 = " << c1.get_count() << endl; //display c1
++c1;
++c1;
++c1;
cout << "c1 = " << c1.get_count() << endl; //display it
--c1;
--c1;
cout << "c1 = " << c1.get_count() << endl; //display it
return 0;
}
Example

9. #include <iostream>
using namespace std;
// Base (Super) Class
class Shape
{
private:
int height;
int width;
public:
Shape() : height(0), width(0)
{ }
Shape(int h, int w) : height(h), width(w)
{ }
int getHeight() const {
return height;
}
int getWidth() const {
return width;
}
void printData() const {
cout << "Height: " << height << endl;
cout << "Width: " << width << endl;
}
};
// Dervied (Sub) Class
class Square : public Shape
{
public:
Square() : Shape()
{ }
Square(int s) : Shape(s, s)
{ }
int getArea() const {
return getHeight() * getWidth();
}
};
// Dervied (Sub) Class
class Rectangle : public Shape
{
public:
Rectangle() : Shape()
{ }
Rectangle(int h, int w) : Shape(h, w)
{ }
int getArea() const {
return getHeight() * getWidth();
}
};
int main()
{
Square s1(5);
Rectangle r1(7, 2);
cout << "Square Area: " << s1.getArea() << endl;
cout << "Rectangle Area: " << r1.getArea() << endl;
return 0;
}
Example

10. The protected Access Specifier
–A protected member can be accessed by member functions in its own
class or in any class derived from its own class.
–It can’t be accessed from functions outside these classes, such as main().

11. #include <iostream>
using namespace std;
class Counter
{
protected: //NOTE: not private
unsigned int count; //count
public:
Counter() : count(0) //constructor, no args
{ }
Counter(int c) : count(c) //constructor, one arg
{ }
unsigned int get_count() const //return count
{
return count;
}
Counter operator ++ () //incr count (prefix)
{
return Counter(++count);
}
};
class CountDn : public Counter
{
public:
CountDn() : Counter() //constructor, no args
{ }
CountDn(int c) : Counter(c) //constructor, 1 arg
{ }
CountDn operator -- () //decr count (prefix)
{
return CountDn(--count);
}
};
int main()
{
CountDn c1; //class CountDn
CountDn c2(100);
cout << "c1 = " << c1.get_count() << endl; //display
cout << "c2 = " << c2.get_count() << endl; //display
++c1; ++c1; ++c1; //increment c1
cout << "c1 = " << c1.get_count() << endl; //display it
--c2; --c2; //decrement c2
cout << "c2 = " << c2.get_count() << endl; //display it
CountDn c3 = --c2; //create c3 from c2
cout << "c3 = " << c3.get_count() << endl; //display c3
return 0;
}
Derived Class
Constructors
The CountDn() constructor calls
the Counter() constructor in the
base class.

12. #include <iostream>
#include <process.h> //for exit()
using namespace std;
class Stack
{
protected: //NOTE: can’t be private
enum { MAX = 3 }; //size of stack array
int st[MAX]; //stack: array of integers
int top; //index to top of stack
public:
Stack() : top(-1) //constructor
{ }
void push(int var) //put number on stack
{
st[++top] = var;
}
int pop() //take number off stack
{
return st[top--];
}
};
class Stack2 : public Stack
{
public:
void push(int var) //put number on stack
{
if (top >= MAX - 1) //error if stack full
{
cout << "\nError: stack is full";
exit(1);
}
Stack::push(var); //call push() in Stack class
}
int pop() //take number off stack
{
if (top < 0) //error if stack empty
{
cout << "\nError: stack is empty\n";
exit(1);
}
return Stack::pop(); //call pop() in Stack class
}
};
int main()
{
Stack2 s1;
s1.push(11); //push some values onto stack
s1.push(22);
s1.push(33);
cout << endl << s1.pop(); //pop some values from stack
cout << endl << s1.pop();
cout << endl << s1.pop();
cout << endl << s1.pop(); //oops, popped one too many...
return 0;
}
Overriding Member
Functions

13. #include <iostream>
using namespace std;
enum posneg { pos, neg }; //for sign in DistSign
class Distance
{
protected: //NOTE: can't be private
int feet;
float inches;
public:
Distance() : feet(0), inches(0.0)
{ }
Distance(int ft, float in) : feet(ft), inches(in)
{ }
void getdist() {
cout << "\nEnter feet: "; cin >> feet;
cout <<"Enter inches: "; cin>>inches;
}
void showdist() const {
cout << feet << "\' - " << inches << '\"';
}
};
class DistSign : public Distance //adds sign to Distance
{
private:
posneg sign; //sign is pos or neg
public:
DistSign() : Distance() //call base constructor
{
sign = pos; //set the sign to +
}
// 2- or 3-arg constructor
DistSign(int ft, float in, posneg sg = pos) : Distance(ft, in) //call base constructor
{
sign = sg; //set the sign
}
void getdist() //get length from user
{
Distance::getdist(); //call base getdist()
char ch; //get sign from user
cout << "Enter sign (+ or -): ";
cin >> ch;
sign = (ch == '+') ? pos : neg;
}
void showdist() const //display distance
{
cout << ((sign == pos) ? "(+)" : "(-)"); //show sign
Distance::showdist(); //ft and in
}
};
int main()
{
DistSign alpha; //no-arg constructor
alpha.getdist(); //get alpha from user
DistSign beta(11, 6.25); //2-arg constructor
DistSign gamma(100, 5.5, neg); //3-arg constructor
//display all distances
cout << "\nalpha = ";
alpha.showdist();
cout << "\nbeta = ";
beta.showdist();
cout << "\ngamma = ";
gamma.showdist();
return 0;
}
Derived Class
Constructors
More Complex Example

15. Class Hierarchies
UML Class Diagram

16. #include <iostream>
using namespace std;
const int LEN = 80; //maximum length of names
class employee //employee class
{
private:
char name[LEN]; //employee name
unsigned long number; //employee number
public:
void getdata()
{
cout << "\n Enter last name: "; cin >> name;
cout << " Enter number: "; cin >> number;
}
void putdata() const
{
cout << "\n Name: " << name;
cout << "\n Number: " << number;
}
};
class manager : public employee //management class
{
private:
chartitle[LEN]; //"vice-president" etc.
double dues; //golf club dues
public:
void getdata()
{
employee::getdata();
cout << " Enter title: "; cin >> title;
cout << " Enter golf club dues: " ; cin >> dues;
}
void putdata() const
{
employee::putdata();
cout << "\n Title: " << title;
cout << "\n Golf club dues: " << dues;
}
};
class scientist : public employee //scientist class
{
private:
int pubs; //number of publications
public:
void getdata()
{
employee::getdata();
cout << " Enter number of pubs: " ; cin >> pubs;
}
void putdata() const
{
employee::putdata();
cout << "\n Number of publications: " << pubs;
}
};
class laborer : public employee //laborer class
{
};
int main()
{
manager m1;
scientist s1;
laborer l1;
//get data for several employees
cout << "\nEnter data for manager 1";
m1.getdata();
cout << "\nEnter data for scientist 1";
s1.getdata();
cout << "\nEnter data for laborer 1";
l1.getdata();
//display data for several employees
cout << "\nData on manager 1";
m1.putdata();
cout <<"\nDataon scientist1";
s1.putdata();
cout << "\nData on laborer 1";
l1.putdata();
return 0;
}
Example
Class Hierarchies

18. #include <iostream>
using namespace std;
class A //base class
{
private:
int privdataA;
protected:
int protdataA;
public:
int pubdataA;
};
class B : public A //publicly-derived class
{
public:
void funct()
{
int a;
a = privdataA; //error: not accessible
a = protdataA; //OK
a = pubdataA; //OK
}
};
class C : private A //privately-derived class
{
public:
void funct()
{
int a;
a = privdataA; //error: not accessible
a = protdataA; //OK
a = pubdataA; //OK
}
};
int main()
{
int a;

B objB;
a = objB.privdataA; //error: not accessible
a = objB.protdataA; //error: not accessible
a = objB.pubdataA; //OK (A public to B)
C objC;
a = objC.privdataA; //error: not accessible
a = objC.protdataA; //error: not accessible
a = objC.pubdataA; //error: not accessible (A private to C)
return 0;
}
publicly- and privately-
derived classes

21. Multiple Inheritance
UML Class Diagram
class A // base class A
{ };
class B // base class B
{ };
class C : public A, public B // C is
derived from A and B
{ };

22. #include <iostre am>
using namespa ce std;
const int LEN = 80; //maximum length of names
class student //educa tional b ackground
{
private:
char sch ool[LEN] ; //n ame of s chool or university
char deg ree[LEN] ; //h ighest d egree earned
public:
void get edu()
{
cout << " Enter name of scho ol or un iversity: " ;
cin >> school;
cout << " Enter highest degr ee earne d (Highschool , Ba chelo r’s, Mas ter’s, PhD): " ;
cin >> degree;
}
void put edu() const
{
cout << "\n Schoo l or uni versity: " << school;
cout << "\n Highe st degre e earned: " << degree;
}
};
class employe e
{
private:
char nam e[LEN]; //employee name
unsigned long number; //emplo yee numb er
public:
void get data()
{
cout << "\n Enter last na me: "; cin >> name;
cout << " Enter number: "; cin >> number;
}
void put data() const
{
cout << "\n Name: " << name;
cout << "\n Numbe r: " << num ber;
}
};
class manager : private employee, pri vate stu dent //m anagemen t
{
private:
chartit le[LE N]; //"vice-preside nt" e tc.
double dues; //g olf club dues
public:
void get data()
{
employee::getdata();
cout << " Enter title: "; cin >> tit le;
cout << " Enter golf club du es: " ; cin >> dues;
student::get edu();
}
void put data() const
{
employee::putdata();
cout << "\n Title : " << title;
cout << "\n Golf club due s: " << due s;
student::put edu();
}
};
class scienti st : pri vate emp loyee, private student //scientist
{
private:
int pubs; //n umber of publications
public:
void get data()
{
employee::getdata();
cout << " Enter number of pu bs: " ; cin >> pubs;
student::get edu();
}
void put data() const
{
employee::putdata();
cout << "\n Numbe r of pub lications: " << pub s;
student::put edu();
}
};
class laborer : public employee //laborer
{ };
int main()
{
manager m1;
scientist s1;
laborer l1;
//get data for sever al emplo yees
cout << "\nEnter dat a for ma nager 1";
m1.getdata();
cout << "\nEnter dat a for sc ientist 1";
s1.getdata();
cout << "\nEnter dat a for la borer 1";
l1.getdata();
//display data for s everal e mployees
cout << "\nData on manager 1";
m1.putdata();
cout <<"\nDataon scientist1";
s1.putdata();
cout << "\nData on laborer 1";
l1.putdata();
return 0;
}
Example

23. private Derivation
–The manager and scientist classes in EMPMULT are privately derived from the
employee and student classes.
–There is no need to use public derivation because objects of manager and
scientist never call routines in the employee and student base classes.
–However, the laborer class must be publicly derived from employer, since it
has no member functions of its own and relies on those in employee.

24. #include <iostream>
#include <string>
using namespace std;
class Person
{
private:
string name;
int age;
public:
Person() : name(""), age(0)
{ }
Person(string n, int a) : name(n), age(a)
{ }
void getPerson() //get person from user
{
cout << "\tEnter name: "; cin >> name;
cout << "\tEnter age: "; cin >> age;
}

void showPerson() const //display type
{
cout << "\tName: " << name << endl;
cout << "\tAge: " << age << endl;
}
};
class Employee
{
private:
string ID;
double salary;
public:
Employee() : ID(""), salary(0.0)
{ }
Employee(string id, double s) : ID(id), salary(s)
{ }
void getEmployee() //get Employee from user
{
cout << "\tEnter ID: "; cin >> ID;
cout << "\tEnter salary: "; cin >> salary;
}
void showEmployee() const //display Employee
{
cout << "\tID: " << ID << endl;
cout << "\tSalary: " << salary << endl;
}
};
class Teacher : public Person, public Employee
{
private:
string rank;
public:
Teacher() : Person(), Employee(), rank("")
{ }
Teacher(string name, int age, string ID, double salary, string r)
: Person(name, age), Employee(ID, salary), rank(r)
{ }
void getTeacher()
{
Person::getPerson();
Employee::getEmployee();
cout << "\tEnter rank: "; cin >> rank;
}
void showTeacher() const
{
Person::showPerson();
Employee::showEmployee();
cout << "\trank: " << rank << endl;
}
};
int main()
{
Teacher t1;
cout <<"Enter Teacher 1 data:\n\n";
t1.getTeacher();
Teacher t2("Ahmed", 38, "1234", 2500, "Excellent");
//display Teacher data
cout << "\n\nTeacher 1:\n";
t1.showTeacher();
cout << "\n\nTeacher 2:\n";
t2.showTeacher();
return 0;
}
Constructors in Multiple
Inheritance

25. #include <iostream>
using namespace std;
class A {
public:
void show() { cout << "Class A\n"; }
};
class B {
public:
void show() { cout << "Class B\n"; }
};
class C : public A, public B
{};
int main() {
C objC; //object of class C
// objC.show(); //ambiguous--will not compile
objC.A::show(); //OK
objC.B::show(); //OK
return 0;
}
Ambiguity in Multiple
Inheritance
1)Two base classes have functions
with the same name, while a class
derived from both base classes
has no function with this name.
How do objects of the derived
class access the correct base class
function?

26. #include <iostream>
using namespace std;
class A {
public:
void func();
};
class B : public A
{ };
class C : public A
{ };
class D : public B, public C
{ };
int main()
{
D objD;
objD.func(); //ambiguous: won’t compile
return 0;
}
Ambiguity in Multiple
Inheritance
2)Another kind of ambiguity arises
if you derive a class from two
classes that are each derived
from the same class.
This creates a diamond-shaped
inheritance tree.

27. #include <ios tream>
#include <str ing>
using namespace std;
class student //educatio nal backgroun d
{
private:
string school; //name of scho ol or unive rsity
string degree; //highest degr ee earned
public:
void getedu()
{
cout << " En ter name of school or university: " ;
cin >> school;
cout << " En ter highest degree earned (Highschool , Bachelor’ s, Master’s, PhD): " ;
cin >> degree;
}
void putedu() co nst
{
cout << "\n School or university: " << school;
cout << "\n Highest degree earned: " << degree;
}
};
class employee
{
private:
string name; //employee name
unsigned long nu mber; //employee number
public:
void getdata()
{
cout << "\n Enter last name: "; cin >> name;
cout << " En ter number: "; cin >> nu mber;
}
void putdata() const
{
cout << "\n Name: " << na me;
cout << "\n Number: " << number;
}
};
class manager //manageme nt
{
private:
string title; // "vice-president" etc.
double dues; //golf club dues
employee emp; // ** object of class employee
student stu; //** object of c lass studen t
public:
void getdata()
{
emp.getdata();
cout << " En ter title: "; cin >> title;
cout << " En ter golf club dues: "; cin >> dues;
stu.getedu() ;
}
void putdata() const
{
emp.putdata();
cout << "\n Title: " << title;
cout << "\n Golf club dues: " << dues;
stu.putedu() ;
}
};
class scientist //scient ist
{
private:
int pubs; //numb er of publications
employee emp; // ** object of class employee
student stu; //** object of c lass studen t
public:
void getdata()
{
emp.getdata();
cout << " En ter number of pubs: "; cin >> pubs;
stu.getedu() ;
}
void putdata() const
{
emp.putdata();
cout << "\n Number of publications: " << pubs;
stu.putedu() ;
}
};
class laborer //laborer
{
private:
employee emp; // object of class employee
public:
void getdata() {
emp.getdata();
}
void putdata() const {
em p.putdata() ;
}
};
int main()
{
manager m1;
scientist s1;
laborer l1;
//get data for sever al employees
cout << "\nEnter data for manager 1";
m1.getdata();
cout << "\nEnter data for scienti st 1";
s1.getdata();
cout << "\nEnter data for laborer 1";
l1.getdata();

//display data for s everal employ ees
cout << "\nData on m anager 1";
m1.putdata();
cout <<"\nDataon scientist1";
s1.putdata();
cout << "\nData on l aborer 1";
l1.putdata();
return 0;
}
Aggregation instead of
inheritance
2)Another kind of ambiguity arises
if you derive a class from two
classes that are each derived
from the same class.
This creates a diamond-shaped
inheritance tree.

28. End of lecture 3
Thank You!