C++ Program Structure

This tutorial describes about program structure of C++ program.

Basically a C++ program involves the following section:

Documentation
Preprocessor Statements
Global Declarations
The main() function
- Local Declarations
- Program Statements & Expressions
User Defined Functions

C++ Program which Outputs a Line of Text

#include <iostream> int main(){ std::cout<<"This is my first C++ Program"; std::cout<<std::endl<<"and its="" very=""></std::endl<<"and></iostream>

1	#include <iostream> int main(){ std::cout<<"This is my first C++ Program"; std::cout<<std::endl<<"and its="" very=""></std::endl<<"and></iostream>

Program Output:

This is my first C++ Programand its very easy.

1	This is my first C++ Programand its very easy.

Let’s look into various parts of the above C++ program:

#include	is a preprocessor directive. It tells the preprocessor to include the contents of iostream header file in the program before compilation. This file is required for input output statements.
int/void	int/void is a return value, which will be explained in a while.
main()	The main() is the main function where program execution begins. Every C++ program should contain only one main function.
Braces	Two curly brackets “{…}” are used to group all statements together.

std::cout<<"This is my first C++ Program";

1	std::cout<<"This is my first C++ Program";

The above line is a statement in C++. A statement must always terminate with a semicolon (;) otherwise it causes a syntax error. This statement introduces two new features of C++ language, cout and << operator.

You will also notice that the words are inside inverted commas because they are what is called a string. Each letter is called a character and a series of characters that is grouped together is called a string. Strings must always be put between inverted commas.

We used std:: before cout. This is required when we use #include .

It specifies that we are using a name (cout) which belongs to namespace std. Namespace is a new concept introduced by ANSI C++ which defines the scope of identifiers which are used in the program. std is the namespace where C++ standard libraries are defined.

Operator << is the insertion stream operator. It sends contents of variable on its right to the object on its left. In our case, right operand is the string “This is my first c++ Program” and left operand is cout object. So it sends the string to the cout object and cout object then displays it on the output screen.

namespace

using namespace std;

1	using namespace std;

If you specify using namespace std then you don’t have to put std:: throughout your code. The program will know to look in the std library to find the object. Namespace std contains all the classes, objects and functions of the standard C++ library.

Example:

 #include <iostream>using namespace std;int main(){ cout<<"This is my first C++ Program."; cout<<std::endl<<"and its="" very=""></std::endl<<"and></iostream>

1	#include <iostream>using namespace std;int main(){ cout<<"This is my first C++ Program."; cout<<std::endl<<"and its="" very=""></std::endl<<"and></iostream>

Return Statement

return 0

At the end of the main function returns value 0.

In new C++ you have to use:

int main() instead of void main()
After you import your headers you required to use using namespace std;
There is no header file like iostream.h, you only required to use this as #include

void main() and iostream.h is only valid for Turbo C++.