Fp201 unit2 1

Unit 2:
Understand the basic structure of C++

 Objectives
 Evolution of C++
 Structure of C++ program
• Preprocessor directives
• Header files
• Main() function
• Return statement
 Hands On!

 At the end of this presentation, you will
be able to:
• Describe the general structure of C++ programs
• Write a simple C++ programme

 Bjarne Stroustrup founded C++ in mid
80’s.
 C++ was developed at AT&T Bell
laboratories.
 Additional features than C.
 Features are closer to the real world
solution.

Include File
(must have)
Class declaration
(if any)
Class Member Function definition
(if any)
Main function
(must have)

Header file Description
<cassert> Contains macros and information for adding
diagnostic that aid program debugging
<cstring> Contains function prototype for C-style string
processing
<cmath> Contains function prototype for math library
function
<iostream> Contains function prototype for standard input
and standard output function
<iomanip> Contains function prototype for stream
manipulator that enable formatting of streams of
data
<fstream> Contains function prototype for functions that
perform input from files on disk and output to files
on disk.

<preprocessor directive>

<main function>
{
<variable declaration>
….
<C++ statement>
….
<return statement(if any)>
}

//First C++ Program Comment
#include <iostream> Preprocessor Directive
using namespace std;
int main() Main Function
{
int a; Variable Declaration
cout << “Hello World!”;
cin >> a; Statement
return 0;
}

 Line 1: // First C++ program
• comment line.
• ignored by the compiler and do not have any
effect on the executable.
• comments in programs help the programmer
(and users) to understand what the program (or
section) does.
• C++ supports two types of comments:
 // line comment

 /* block comment */

 Line 2: #include <iostream>
• lines beginning with a hash (or pound) sign (#) are
directives for the preprocessor.
• runs before the compiler each time the compiler is
invoked.
• translates any line that begins with a hash symbol
(#) into a special command, getting your code file
ready for the compiler.
• #include <iostream> tells the preprocessor to
include the iostream standard file which contains the
declarations of the basic standard input-output
library in C++.

 Line 3: using namespace std;
• namespace allows to group entities like variables,
classes, objects and functions under a name.
• elements belonging to the standard C++ library are
declared in what is called a std namespace.
• example: cout is defined under std namespace
where you can see the details in the file <iostream>.
• if you omit this line, in order to use cout, you need to
write the name of the namespace (std) followed by
scope operator (::) before cout.
 Eg: std::cout << "Hello world!";.

 Line 4: empty line
• An empty line does nothing except for help the
programmer to view the source code more
clearly.

 Line 5: int main()
• actual program starts must start with a function
named main().
• every C++ program has only one main()
function.

 Lines 6 and 11:
 The body of the main() function is enclosed in braces ({ }).

 Line 8: cout << "Hello World!";
 this line is a C++ statement which performs the only
action that generates a visible effect in our first program.
 Each statement must end with a semicolon character (;).
 Here's how cout is used: type the word cout, followed by
the output insertion (or redirection) operator (<<).
 Whatever follows the output insertion operator is output
to the screen.
 If you want to output a string of characters be sure to
enclose them in double quotes (" "), as shown on line 7,
"Hello World!".

 Line 10: return 0;
• return statement causes the main() function (i.e.
the program) to finish.

 Write a program that outputs following
lines to the screen:

Welcome to the world of C++

#include <iostream>

void main( )
{
cout << “Welcome to the world
of C++”
}

 Why does the following program fail?

#include <iostreams>

void main()
{
cout << “Is there a bug
here?”;
}

 Because of the typo error for the
preprocessor directive
 Wrong : iostreams
 Correct: iostream

 Explain why we use std:: in the following program.
What is the output of program?
#include <iostream>
void main()
{
std::cout << " ## # # "<< std::endl;
std::cout << "# ### ###"<<std::endl;
std::cout << " ## # # "<< std::endl;
}

Fp201 unit2 1

Related slideshows

More Related Content

Fp201 unit2 1