Structure of C++ Program
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
|
