This document discusses the basic structure of C++ programs. It covers preprocessor directives, header files, the main function, and return statements. It provides examples of a simple Hello World program structure and explains each part. It also lists common C++ header files and their purposes.

1. Unit 2:
Understand the basic structure of C++

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

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

4.  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.

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

6. 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.

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

8. //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;
}

9.  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 */

10.  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++.

11.  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!";.

12.  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.

13.  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!".

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

15.  Write a program that outputs following
lines to the screen:
Welcome to the world of C++

16. #include <iostream>
using namespace std;
void main( )
{
cout << “Welcome to the world
of C++”
}

17.  Why does the following program fail?
#include <iostreams>
using namespace std;
void main()
{
cout << “Is there a bug
here?”;
}

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

19.  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;
}

20.  Refer to slide 11