First program is C++ 
// This is my first program is C++
/* this program will illustrate different components of
a simple program in C++ */
#include <iostream>
using namespace std;
int main()
{
cout << "Hello World!";
return 0;
}When the above program is compiled, linked and executed, the following output is displayed on the VDU screen.
Hello World!
Various components of this program are discussed below:
Comments
First three lines of the above program are comments and are ignored by the compiler. Comments are included in a program to make it more readable. If a comment is short and can be accommodated in a single line, then it is started with double slash sequence in the first line of the program. However, if there are multiple lines in a comment, it is enclosed between the two symbols /* and */
#include <iostream>
The line in the above program that start with # symbol are called directives and are instructions to the compiler. The word include with '#' tells the compiler to include the file iostream into the file of the above program. File iostream is a header file needed for input/ output requirements of the program. Therefore, this file has been included at the top of the program.
using namespace std;
All the elements of the standard C++ library are declared within std. This line is very frequent in C++ programs that use the standard library.
int main ( )
The word main is a function name. The brackets ( ) with main tells that main ( ) is a function. The word int before main ( ) indicates that integer value is being returned by the function main (). When program is loaded in the memory, the control is handed over to function main ( ) and it is the first function to be executed.
Curly bracket and body of the function main ( )
A C++ program starts with function called main(). The body of the function is enclosed between curly braces. The program statements are written within the brackets. Each statement must end by a semicolon, without which an error message in generated.
cout<<"Hello World!";
This statement prints our "Hello World!" message on the screen. cout understands that anything sent to it via the << operator should be printed on the screen.
return 0;
This is a new type of statement, called a return statement. When a program finishes running, it sends a value to the operating system. This particular return statement returns the value of 0 to the operating system, which means “everything went okay!”.
Printing Multiple Lines of Text with a Single Statement
/* This program illustrates how to print multiple lines of text with a single statement */
#include <iostream>
using namespace std;
int main()
{
cout << "Welcome\nto\nC++";
return 0;
}
Output:
Welcome
to
C++
The characters print exactly as they appear between the double quotes. However, if we type \n, the characters \n are not printed on the screen. The backslash (\) is called an escape character. It indicates that a "special" character is to be output. When a backslash is encountered in a string of characters, the next character is combined with the backslash to form an escape sequence. The escape sequence \n means newline. It causes the cursor to move to the beginning of the next line on the screen.
The following table gives a listing of common escape sequences.
| Escape Sequence | Description |
| \n | Newline |
| \t | Horizontal tab |
| \a | Bell (beep) |
| \\ | Backslash |
| \' | Single quote |
| \'' | Double quote |