Oop lec 2(introduction to object oriented technology)

Introduction to Object Technology,
Introduction to C++ Programming
Lecture No 2
COMSATS Institute of Information & Technology

Reference Books:
Object Oriented Programming in C++, Robert Lafore
C++ How to Program, Deitel & Deitel
Object oriented programming, Ashok N. Kamthane

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COMSATS Institute of Information Technology
Object Oriented Programming

High-level Languages
Common programming languages include …

C C++ Java Pascal Visual Basic FORTRAN
COBOL Lisp Scheme Ada
These high – level languages
Resemble human languages
Are designed to be easy to read and write
Use more complicated instructions than
the CPU can follow
Must be translated to zeros and ones for the CPU
to execute a program
3


Low-level Languages
An assembly language command such as

ADD X Y Z
might mean add the values found at x and y
in memory, and store the result in location z.
Assembly language must be translated to

machine language (zeros and ones)
0110 1001 1010 1011
The CPU can follow machine language
4


5


Compilers
Translate high-level language to

machine language
Source code
 the original program in a high level language

Object code
 the translated version in machine language

6


Linkers
Some programs we use are already compiled
Their object code is available for us to use
For example: Input and output routines

A Linker combines
The object code for the programs we write

and
The object code for the pre-compiled routines
into
The machine language program the CPU can run

7


Programming
and Problem Solving
Algorithm
A sequence of precise instructions which

leads to a solution
Program
An algorithm expressed in a language the computer

can understand

8


Program Design
Programming is a creative process
No complete set of rules for creating a program

Program Design Process
Problem Solving Phase
 Result is an algorithm that solves the problem

Implementation Phase
 Result is the algorithm translated into a programming

language

9


Problem Solving Phase
Be certain the task is completely specified
What is the input?
What information is in the output?
How is the output organized?

Develop the algorithm before implementation
Experience shows this saves time in getting your

program to run.
Test the algorithm for correctness

10


Implementation Phase
Translate the algorithm into a programming

language

Easier as you gain experience with the language

Compile the source code
Locates errors in using the programming language
Run the program on sample data
Verify correctness of results
Results may require modification of

the algorithm and program

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Procedural Languages
•

•
•
•
•

Examples of procedural languages: C, Pascal, Fortran
A program in a procedural language is basically
a list of instructions
As programs become larger they are usually broken down
into smaller units, such as functions, procedures, subroutines
Functions can be grouped together into modules according
to their functionality, objectives and tasks.
Structured programming is a programming paradigm that
to a large extent relies on the idea of dividing a program
into functions and modules.

13


Problems with Structured Programming
• Functions have unrestricted access to global data
Function A:

Function B:

Function C:

local data

local data

local data

global data X

global data Y

• Large number of potential connections between functions and
data (everything is related to everything, no clear boundaries)
• makes it difficult to conceptualize program structure
• makes it difficult to modify and maintain the program
e.g. : it is difficult to tell which functions access the data
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global data Z

Problems with Structured Programming
• data

and function are considered as two separate
entities
• makes it difficult to model things in the real world
• complex real world objects have both attributes and
behaviours
• attributes
• people: name, date of birth, eye color, job title
• cars: horse power, number of doors, color
• behaviours
• people: ask a person to bring you a beer
• cars: apply the brakes, turn on the engine
• attributes and behaviors alone are sufficient to realistically
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model real world objects but a unified view is needed

Object Oriented
Programming
Abbreviated OOP
Used for many modern programs
Program is viewed as interacting objects
Each object contains algorithms to describe its behavior
Program design phase involves designing objects and

their algorithms

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OOP Characteristics
Encapsulation
Information hiding
Objects contain their own data and algorithms
Inheritance
Writing reusable code
Objects can inherit characteristics from other objects
Polymorphism
A single name can have multiple meanings depending
on its context
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Object Oriented Approach
Object
functions

data

• Encapsulation: integrate data and functions into one object
• Data hiding : data is hidden to the outside world and can
only be accessed via the functions
• In C++ functions are called membership functions in other
languages they are called methods
• Data items are called attributes or instance variables
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Object Oriented Approach
• separation: objects interact with each other only via their membership functions
• separation helps to maintain the integrity of the entire
program

Object A
functions

Object C
functions

data
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data

Object B
functions

data

Abstraction
• An abstraction is a named collection of attributes and
behavior relevant to model a given entity for some
particular purpose
real-world

abstraction

attributes

software

{data, data,…}

entity

behavior
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{ method, method…}

Separation
• independent specification of a visible interface and
a hidden implementation
• interface is some kind of contract between the object
and the user of this object or module
• separation is not restricted to object-oriented programming
for example header files in standard C can be regarded
as interfaces

visible

hidden
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interface

Implementation

Structure of an Object
Implementation

Interface

Object
method

method

code

code
data

method
method
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code
code


Examples of Objects

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• physcial objects
• vehicles in a traffic-flow simulation
• electrical components in a circuit-design program
• elements of a computer user environment
• menus
• graphic objects
• data-storage constructs
• arrays
• linked lists
• human entities
• employees
• students
• collections of data
• an inventory
• an address book
• user defined data types
• time
• complex numbers

Example of a Class in C++
class someobject
//declares a class
{
private:
int somedata;
//class data
public:
void setdata(int d) //membership function to set data
{ somedata=d; }
int getdata()
//membership function to get data
{ return somedata; }
}
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Classes versus Objects
• A class is a prototype specification from which
one can generate a number of similar objects
• A class can be considered as an object factory.
• An object is said to be a member or instance of a class
• A class can be considered as a more complex
data structure than an ordinary built-in data type
• Standard C already knows the struct command for
user defined data types:
struct complex
{
double re;
double im;
};
complex x;

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Instantiation of Objects
person
data: name, p_nummer, address, date of birth
methods: getage(), changeaddress(newaddress)

Class

person
data: Lena Brat, 761203-7111, Stureplan 4, female
person
data: Erik Olsson, 780605-4789, Hamngatan 3, male
person
data: Lars Backe, 671110-A562, Mälartorget 19, male
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Relationships among Objects
• Attribute:

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One object uses as another object as an attribute,
namely as member data, for example a Person
contains an attribute Name. This type of relationship is also called a weak association or has-a
relationship. Example: A Person has a Name
• Association:
One object uses another to help it carry out a task.
Classes that collaborate are usually related through
associations. This type of relationship is also
called a uses relationship.
Example: The object Driver invokes
the method Brake
Object Oriented Programming of the object BrakingSystem.

• Aggregation:
Aggregation means that one object contains other
objects. Aggregation is also called part-of relationship.
Example: The class Adressbook contains many People
Objects.
• Composition:

Composition is building objects from parts. It is a stronger
type of aggregation in which the parts are necessary to
the whole, namely they are permanently bound to the
object and do not exist outside the object.
A class Processor contains a CPU, Memory and I/O-Ports.
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• Generalization

Generalization is a relationship defined at the class level
not the object level, which means that all objects of
this class must obey the relationship. This is type of
relationship is also called a is-a-kind-of relationship.
Generalization in object oriented languages is realized
by means of inheritance.
Example: A car is a kind of vehicle.

29


Inheritance
• In our daily lives we use the concept of classes divided
into subclasses, for example vehicles are divided into cars,
trucks, buses and motor cycles.
• The principle in this sort of division is that each sub-class shares
some common features with the base class from which it
is derived, but also has its own particular features.

base class
Vehicle
wheels
engine
Car

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wheels
sub-classes or
engine
COMSATS Institute of Information Technologyderived classes
trunk
trunk

Truck
wheels
engine
trailer
trailer

Inheritance
• A sub-class also shares common methods with its
super-class but can add its own methods or overwrite
the methods of its super-class.

base class
Vehicle
brake()
start_engine()
Car
brake()
start_engine()
open_door()
open_door()
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Truck
sub-classes or
derived classes

brake()
start_engine()
open_door()
pull_trailer()

Inheritance
Terminology:
• Car is a sub-class (or derived class) of Vehicle
• Car inherits from Vehicle
• Car is a specialization of Vehicle
• Vehicle is a super-class (or base class) of Car
• Vehicle is a generalization of Car
• In C++ an object of a sub-class is substitutable
for an object of the super-class, in other words
an object of class Car can be used whenever
an object of class Vehicle is required.
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Reusability
• Reusability means

that a class that has been designed,
created and debugged once can be distributed to other
programmers for use in their own programs.
• Similar to the idea of a library of functions in a procedural
language.
• The concept of inheritance provides an important extension
to the idea of reusability, as it allows a programmer to take
an existing class without modifying it and adding additional
features and functionality. This is done by inheriting a new
sub-class from the exisiting base class.

33


Polymorphism & Overloading
• Polymorphism : using functions and operators in different
ways, depending on what they are operating on.
• Polymorphism allows it to manipulate objects without
knowing their exact type but only their common property.
for example, the classes Triangle and Circle both
have their own (polymorphic) version of the method Draw,
but a graphic routine that draws graphical elements does
not have to know which object it manipulates.
• Overloading: an existing operator, such as + or = is given
the capability to operate on a new data type, for example
define the operator + for the class Complex such that
it realizes the addition of two complex numbers.
34


Polymorphism
• polymorphism means ”having many shapes”
• in C++ it refers to a situation in which an object
could have any of several types
• a polymorphic variable can refer to objects of
different classes, for example a graphic object can
be either a circle or a triangle
• a polymorphic function or operator can take arguments of
different types
• example:
int max(int a, int b);
double max(double a, double b);
35


C++ and C

36

• C++ is derived from the language C
• C++ is a superset of C, that means almost every
correct statement in C is also correct in C++
• The most important elements added to C are concerned
with classes, objects and object-oriented programming
• New features of C++
• improved approach to input/output
• standard template library (STL)
container classes for vectors, lists, maps, etc.
• reference type replaces pointers
• const variables replaces #define statements
• string data type replaces C-style strings char[]
• new comment style augments C-style comments /* */

Software Life Cycle
1.
2.
3.
4.
5.

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Analysis and specification of the task
(problem definition)
Design of the software
(object and algorithm design)
Implementation (coding)
Maintenance and evolution of the system
Obsolescence


C++ History
C developed by Dennis Ritchie at AT&T

Bell Labs in the 1970s.

Used to maintain UNIX systems
Many commercial applications written in c

C++ developed by Bjarne Stroustrup at AT&T

Bell Labs in the 1980s.

Overcame several shortcomings of C
Incorporated object oriented programming
C remains a subset of C++

38


C++ Standard Library
C++ programs
Built from pieces called classes and functions

C++ standard library
Rich collections of existing classes and functions

“Building block approach” to creating programs
“Software reuse”

39


Basics of a Typical C++ Environment
C++ systems
Program-development environment
Language
C++ Standard Library

40


Basics of a Typical C++ Environment
Editor

Phases of C++ Programs:
1. Edit
2. Preprocess
3. Compile
4. Link
5. Load
6. Execute

Program is created in
the editor and stored
on disk.

Disk

Preprocessor

Disk

Preprocessor program
processes the code.

Compiler

Disk

Compiler creates
object code and stores
it on disk.

Linker

Disk

Loader

Disk

Primary
Memory

Linker links the object
code with the libraries,
creates a.out and
stores it on disk

Loader puts program
in memory.
.
.
.
.
.
.

Primary
Memory

CPU

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.
.
.
.
.
.

CPU takes each
instruction and
executes it, possibly
storing new data
values as the program
executes.

A Sample C++ Program
A simple C++ program begins this way

#include <iostream>
using namespace std;
int main()
{
Statements;
}

42

return 0;


#include <iostream>
int main()
{
cout << “Hello Worldn”;
return 0;
}

43


Example: Adding Two Integers
#include <iostream>
// function main begins program execution
int main()
{
int integer1; // first number to be input by user
int integer2; // second number to be input by user
int sum;

// variable in which sum will be stored

cout << "Enter first integern"; // prompt
cin >> integer1;

// read an integer

cout << "Enter second integern"; // prompt
cin >> integer2;

// read an integer

sum = integer1 + integer2; // assign result to sum
cout << "Sum is " << sum << endl; // print sum
return 0; // indicate that program ended successfully
}

44


Variables
Location in memory where value can be stored
Common data types
 int - integer numbers
 char - characters
 double - floating point numbers
Declare variables with name and data type before use
int integer1;
int integer2;
int sum;
Can declare several variables of same type in one declaration
 Comma-separated list
int integer1, integer2, sum;
45


Variables
Variable names
 Valid identifier
 Series of characters (letters, digits, underscores)
 Cannot begin with digit
 Case sensitive

46


Input stream object
>> (stream extraction operator)
 Used with cin
 Waits for user to input value, then press Enter (Return) key
 Stores value in variable to right of operator
 Converts value to variable data type

 = (assignment operator)
 Assigns value to variable
 Binary operator (two operands)
 Example:

sum = variable1 + variable2;

47


 Comments

Document programs
Improve program readability
Ignored by compiler
Single-line comment
 Begin with //

 Preprocessor directives

Processed by preprocessor before compiling
Begin with #

Include Directives

#include <iostream>

Tells compiler where to find information about items

used in the program
iostream is a library containing definitions of cin and cout
48


 Standard output stream object

cout
“Connected” to screen
<<
 Stream insertion operator
 Value to right (right operand) inserted into output stream

 Namespace

Tells the compiler to use names in iostream in

a “standard” way
std:: specifies using name that belongs to “namespace” std
std:: removed through use of using statements
 Escape characters


Indicates “special” character output

49


Running a C++ Program
C++ source code is written with a text

editor

The compiler on your system converts

source code to object code.

The linker combines all the object code

into an executable program.

50


51


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1.4

Testing and Debugging
Bug
A mistake in a program

Debugging
Eliminating mistakes in programs
Term used when a moth caused a failed relay

on the Harvard Mark 1 computer. Grace Hopper
and other programmers taped the moth in logbook
stating:
“First actual case of a bug being found.”

53


Program Errors
Syntax errors
Violation of the grammar rules of the language
Discovered by the compiler
 Error messages may not always show correct location of

errors

Run-time errors
Error conditions detected by the computer at run-time
Logic errors
Errors in the program’s algorithm
Most difficult to diagnose
Computer does not recognize an error
54


Escape Sequence
n

Newline. Position the screen cursor to the
beginning of the next line.

t

Horizontal tab. Move the screen cursor to the next
tab stop.

r

Carriage return. Position the screen cursor to the
beginning of the current line; do not advance to the
next line.

a

Alert. Sound the system bell.

Backslash. Used to print a backslash character.

"

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Description

Double quote. Used to print a double quote
character.


Oop lec 2(introduction to object oriented technology)

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