This document discusses object-oriented programming in C++. It covers the basics of C++ including the creation of classes with public and private access specifiers, defining member functions inside and outside of classes, and creating objects of a class. Examples are provided of simple C++ programs and the general structure of a C++ program. The document also notes that C++ is a multi-paradigm language created by Bjarne Stroustrup in 1983.

1. Lecture 3
CSE1201: Object Oriented
Programming-I (C++)

2. 9/5/2023 2
Paradigm: Multi-paradigm
Creator: Bjarne Stroustrup
First appeared: 1983

3. C++ Program Execution Flow
9/5/2023 3

4. A First C++ Program
#include <iostream>
using namespace std;
// main() is where program execution begins
int main() {
// prints Hello World
cout << "Hello World";
return 0;
}
9/5/2023 4

5. A First C++ Program
• Save the program as first.cpp
• Build and Run the code
9/5/2023 5

6. Another C++ Program
#include <iostream>
using namespace std;
int main() {
int num;
cin >> num;
cout << "number: " <<num << endl;
return 0;
}
9/5/2023 6

7. The General Form of a Class in C++
 A class is defined by specifying the data and the
code that operate on the data
 The general form:
class classname{
private data and functions declarations
access-specifier:
data and functions declarations
access-specifier:
data and functions declarations
};
7
9/5/2023

8. Example
class person
{
int age;
public:
void display_age()
{
cout << age;
}
};

9. The General Form of a Class in C++
• Functions that are declared within a class are
called member functions
• Member functions may access any element of the
class of which they are a part, this includes all
private elements
• Variables that are elements of a class are called
member variables or data members. (The term
instance variable is also used)
9
9/5/2023

10. Access specifier
• access-specifier is one of these three C++ keywords:
– public
– private
– Protected
• (access-specifier is also known as visibility label)
• By default, functions and data declared within a class
are private to that class and may be accessed only by
other members of the class
9/5/2023 10

11. Access specifier
 The public access-specifier allows functions or data
to be accessible to other parts of your program
 The protected access-specifier is needed only when
inheritance is involved
 Once an access-specifier has been used, it remains in
effect until either another access-specifier is
encountered or the end of the class declaration is
reached
11

12. Access specifier
• In general, you should make all data members of a
class private to that class.
– This is part of the way that encapsulation is achieved
• However, there may be situations in which you will
need to make one or more variables public
12

13. Creating Objects
 Once a class has been declared, we can create
variables (object) of that type by using the class
name (like any other built in variables)
 The necessary memory space is allocated to an
object at this stage
 Class specification provides only a template and
does not create any memory space for the members
 Format: class_name object_name;
 Example: person p;
13
9/5/2023

14. Creating Objects
 Objects can also be created when a class is defined
by placing their names immediately after the closing
brace.
class class_name
{
} x, y, z;
 Each object contains its own copy of each instance
variables defined by the class
14
9/5/2023

15. Accessing class members
 The private data of a class can only be
accessed only through the member functions
of that class
 Following is the format for accessing a
member
Object_name.function_name(arguments)
Object_name.variable_name
9/5/2023 15

16. Defining member functions
 Member functions can be defined in two
places:
 Outside the class definition
 Inside the class definition
 Irrespective of the place of definition, the
function will perform the same task
9/5/2023 16

17. Outside the class definition
 Member functions that are only declared inside of a
class, have to be defined separately outside the class
 General format of a member function definition outside
the class is
return_type class_name:: function_name (arguments)
{
}
 The membership label class_name:: tells the compiler
that, function function_name belongs to the class
class_name
 The symbol :: is called the scope resolution operator
9/5/2023 17

18. Inside the class definition
 Another method of defining a member function is to
replace the function declaration by the actual
function definition inside the class definition
 Usually, only small functions are defined inside the
class definition
9/5/2023 18

19. General structure of a c++ program
Include files
Class declarations
Member functions definitions
Main function program
9/5/2023 19

20. Thank you