Structure of C++ Program

A C++ program consist four sections as shown in following fig.This section may be placed in a separate code files and then compiled independently or jointly.

Section I : Header File Declaration Section
  1. Header Files used in the program are listed here.
  2. Header files provides prototype declarations for different library functions.
  3. Basically all preprocessor directives are written in this section.

Section II : Global Declaration Section
  1. Global Variables are declared here.
  2. Global Declaration include
       Declaring structure
       Declaring class
       Declaring variable.

Section III : Class Declaration Section 
   1. Actually this section can be considered as a sub section for the global declaration section.
   2. Class declaration and all method of that class are defined here.

Section IV : main Function
  1. Each and every cpp program always starts with main function.
  2. This is the entry point for the functions.Each and every method is called indirectly through main.
  3.We can create class object in the main.
  4. Operating system call this function automatically.

This approach is based on client server model as shown in figure.
  This class definition including member function constitute the server that provides the service to the main program known as a client.
  Client uses the server through public interface class.

Simple C++ Program
//Program to print String
#include<conio.h>
#include<iostream.h>
class first
{
  public:
  void display()
  {
   cout<<"Welcome to the world of C++";
   }
};
 void main()
 {
  first f;
  f.display();
  getch();
}

Output-
    Welcome to the world of C++