Oop l2

OOP
Lecture-2
Dr. Mohammad Shahidul Islam
Assistant professor

2.1 What is C++
• Its an OOP Language
• Introduced by AT&T bell laboratory in 1980’s
• Still retains the power of C
• Initially it was named as “C with classes”
• C++ is a superset of C
• Some differences will prevent the C to run in
the C++ compiler
DMSI 2

2.1 What is C++
• Important features added over C are classes,
inheritance, function overloading and
operator overloading.
• C++ allows programmers to build large
programs with clarity, extensibility, and ease
of maintenance incorporating the spirit and
efficiency of C
• It facilitates(সহজসাধ্য করে ত ালা) bottom up
approach which was top down in case of C
DMSI 3

Applications of OOP
• OOP language like C++ or JAVA is capable of
handling large programs easily
• Task includes development of editors,
compilers, databases, communication systems
and any complex real time systems
DMSI 4

Applications of OOP
• Since C++ allows us to create hierarchy-related
objects, we can build special object oriented
libraries which can be used later by many
programmers.
• While C++ is able to map the real-world problem
properly, the C part of C++ gives the language the
ability to get close to the machine-level details.
• C++ programs are easily maintainable and
expandable. When a new feature needs to be
implemented, it is vary easy to add to the exiting
structure of an object.
DMSI 5

2.3 A Simple C++ Program
• Printing a string
# include <iostream> // include header file
using namespace std;
Int main()
{
Cout<< “my name is ………..”; //C++ statement
Return 0;
} // end of example
• Program Features
– only one function, main(). //can have more
– Like C the C++ statements terminate with semicolons
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Example (cont.)
• Comments
– C++ introduces a new comment symbol //
– Note that there is no closing symbol
• for*(j=0; j<n; /* loops n times */ J++)
– Can we use double slash?
• Output Operator:
• two ne C++ features, cout and <<.
• The operator << is called the insertion or put to
operator
DMSI 7

Output Operator:
• You may recall that the operator << is the bit-wise left-
shift operator and it can still be used for this purpose.
• This is an example of how one operator can be used for
different purposes, depending on the context.
• This concept is known an operator overloading, an
important aspect of polymorphism.
DMSI 8

The iostream File
• We have used the following #include directive in
the program;
– # include <iostream>
• This directive causes the preprocessor to add the
contents of the iostream file to the program.
• It contains declarations for the identifier cout and
the operator «.
• Some old versions of C++ use a header file called
ioslream.h.
• This is one of the changes introduced by ANSI
C++.
DMSI 9

Return Type of main ( )
• In C++, main() returns an integer type value to the operating
system.
• Therefore, every main() in C + + should end with a return(O)
statement; otherwise a warning or an error might occur.
• Since main() returns an integer type value, return type for main() is
explicitly specified as int. Note that the default return type for all
functions in C++ is int.
• The following main without type and return will run with a warning:
• main()
{
-----
-----
}
DMSI 10

More C+ + Statements
#include<iostream>
int main()
{
float v1,v2,sum, average;
cout<< "entr the numversn";
cin>> v1;
cin>> v2;
sum=v1+v2;
average=sum/2;
cout<< "sum= "<<sum<<"n";
cout<< "average= "<<average<<"n";
return 0;
}
DMSI 11

• Variables?
• Input Operator?
• Cascading of I/O Operators?
– cout<< "sum= "<<sum<<"n";
– The multiple use of << in one statement is called
cascading
• What is the difference,
cout<< "sum= "<<sum<<“,"
<< "average= "<<average<<"n";
DMSI 12

Class
#include <iostream>
class person
{
char name[30];
int age;
public:
void getdata(void);
void display(void);
};
void person:: getdata(void)
{
cout<<"enter the namen";
cin>> name;
cout<<"enter the agen";
cin>>age;
}
void person:: display(void)
{
cout<<"Name of the person:
"<<name<<"n";
cout<<"Age of the person:
"<<age<<"n";
}
int main()
{
person p;
p.getdata();
p.display();
return 0;
}

Class (cont.)
• Class person has two two functions called
member function.
• The main program uses person to declare
variables of its type.
• Here P is an object of type person.

Classes in Java:
public class Dog
{
String breed;
int age;
String color;
void barking(){ }
void hungry(){ }
void sleeping(){ }
}

Structure of C++ program
• The previous OOP code shows that a typical
code can have four sections….
– Include files
– Class declaration
– Member functions definition
– Main function program

Client-Server model
• The class definition includinf the member
functions are known as server and
• The main function is know as client

Creating source file
• In C++ we can use text editor to create it
• In UNIX we can use vi or ed editor
• In dos we can use edlin
• The created file should have appropritae
extension to be recognised.

Compiling and Linking
• The process of compiling and linking again
depends upon the operating system.
• Each system has its own command to run.
DMSI 19

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