Introduction to Header Files

C++ is a huge language so much that it uses various sets of instructions from different parts to do its work. Some of these instructions come in computer files that you simply "put" in your program. These instructions or files are also called libraries. To make your job easier, some of these libraries have already been written for you so that as you include them in your program, you already have a good foundation to continue your construction. Yet, some of these libraries have their limitations, which means you will expand them by writing or including your own libraries.

As noted already, there are libraries previously written for you. One of them asks the computer to receive keyboard strokes from you the user (when you press a key) and another asks the machine (the computer performing some operations) to give back a result. The libraries are files that you place at the beginning of your program as if you were telling the computer to receive its preliminary instructions from another program before expanding on yours. The libraries are (also) called header files and, as computer files, they have the extension ".h". An example would be house.h, or person.h. As you see, they could have any name; when you start creating your own libraries, you will give your files custom and recognizable names.

The first library we will be interested in is called iostream. It asks the computer to display stuff on the monitor's screen.

To see how to put a library in your program, you put it at the beginning of the file. Here is an example:

iostream.h

To use a library in your program, you simply include it by using the word "include" before the name of the library, as follows:

include iostream.h

Since this is a computer language, the computer will follow particular instructions to perform appropriately, which will make this language distinct from the everyday languages. C++ has some words it treats specially and some that will completely depend on you the programmer. For example, the word "include" could be a special word used by C++ or a regular you want to use in your program. In this particular situation, if you want the computer to "know" that the word "include" means, "I want to include the following library", you will have to append a special sign to it. The pound sign "#" will do just that. Therefore, to include a library, you precede the include word with the # sign.

Here is an example:

#include iostream.h

There are usually two kinds of libraries or files you will use in your programs: libraries that came with C++, and those that you write. To include your own library, you would enclose it between double quotes, like this

#include "books.h"

When you include a library that came with C++, you enclose it between < and > as follows:

#include 

Following this same technique, you can add as many libraries as you see fit. Before adding a file, you will need to know what that file is and why you need it. This will mostly depend on your application. For example, you can include a library called stdio like this:

#include 
#include 

 

Introduction to Namespaces

A namespace is a section of code, delimited and referred to using a specific name. A namespace is created to set apart a portion of code with the goal to reduce, otherwise eliminate, confusion. This is done by giving a common name to that portion of code so that, when referring to it, only entities that are part of that section would be referred to.

Because C++ is so huge, its libraries are created in different namespaces, each with a particular name. To use an existing namespace in your program, you must know its name. To use such a namespace, you can type the using namespace expression followed by the name of the namespace and a semi-colon. For example, to use a namespace called django, you would type:

using namespace django;

One of the namespaces used in C++ is called std. Therefore, to use it, you can type:

using namespace std;

After typing this, any part of the namespace becomes available to you. The iostream library we mentioned above is part of the std namespace. When you use it, you don't need to include the extended of the iostream file. For this reason, you can start your program with:

#include 
using namespace std;