Introduction to Computers
Overview
A computer is a machine that receives instructions and produces a result after performing an appropriate assignment. Since it is a machine, it expects good and precise directives in order to do something. The end result depends on various factors ranging from the particular capabilities of the machine, the instructions it received, and the expected result.
As a machine, the computer cannot figure out what you want. The computer doesn't think and therefore doesn't make mistakes.
Computer programming is the art of writing instructions (programs) that ask the computer to do something and give a result. A computer receives instructions in many different forms, four of which are particularly important.
The first instructions are given by the manufacturers of various hardware parts such as the microprocessor, the motherboard, the floppy and the CD-ROM drives, etc. These parts are usually made by different companies, setting different and various goals that their particular part can perform. The instructions given to the microprocessor, for example, tell it how to perform calculations, at what speed, and under which circumstances. The instructions given to the motherboard tell it to behave like a city where people and cars can move from one part of the town to another, back and forth, for various reasons; this allows information to flow from one part of the city, I mean one section of the computer, to another.
Once the instructions given to the hardware parts are known, software engineers use that information to give the second sets of instructions to the computer. These instructions, known as an operating system, are usually written by one company. These second instructions tell the computer how to coordinate its different components so the result will be a combination of different effects. This time, the computer is instructed about where the pieces of information it receives are coming from, what to do with them, then where to send the result. This time also the operating system designers impose a lot of behaviors to the computer as a machine. Again this time, some computer languages are developed so that programmers can write applications as the third set of instructions. It is like developing languages that people in a city can use to talk to each other. Consider that from now on (once the OS is developed), people get into the habit of doing things according to their particular culture or taste, speaking different languages that their neighbor doesn't understand... Luckily, the computer, I should say the OS, understands all these languages (I can't guaranty that). Some of the operating systems on the market are: Microsoft Windows 3.X, Corel Linux, IBM OS2, Microsoft Windows 9X, Apple OS 10, Red Hat Linux, Microsoft Windows Millennium, BeOS, Caldera Linux, Microsoft Windows 2000 etc. A particular OS (for example Microsoft Windows 98) depending on a particular processor (for example Intel Pentium) is sometimes referred to as a platform. Some of the computer languages running on Microsoft Windows operating systems are C++, Pascal, Basic, and their variants.
The actual third set of instructions are given to the computer by you, the programmer, using one or more of the languages that the operating system you are planning to use can understand. Your job is going to consist of writing applications. As a programmer, you write statements such as telling the computer, actually the operating system, that "If the user clicks this, do the following, but if he clicks that, do something else. If the user right clicks, display this; if he double-clicks that, do that." To write these instructions, called programs, you first learn to "speak" one of the languages of the OS. Then, you become more creative... Some of the application programs in the market are Microsoft Word, Lotus ScreenCam, Adobe Acrobat, Jasc Paint Shop Pro, etc.
The last instructions are given by whoever uses your program, or your application. For example, if you had programmed Microsoft Word, you would have told the computer that "If a user clicks the New button on the Standard toolbar, I want you to display a new empty document. But if the user clicks File -> New..., I want you to 'call' the New dialog and provide more options to create a new document. If the same user right-clicks on any button on any of the toolbars, I want you to show, from a popup menu, all the toolbars available so she can choose which one she wants. But if she right-clicks on the main document, here is another menu I want you to display."
At this time, you have probably realized that the users of your programs depend on your techniques as a developer to provide an easy to use application (that's what recruiters and employers call experience and creativity). You depend on the computer language that you are actually using (every computer language has its ups and downs). Your computer language depends on the operating system it is running on (different
operating systems have different strengths and weaknesses). The operating system depends on the microprocessor or the machine it is running in (the biggest difference between two microprocessors is the speeds at which each processes information).
Your interest here is on the computer languages, since you are going to write programs. There are various computer languages, for different reasons, capable of doing different things. Fortunately, the computer can distinguish between different languages and perform accordingly. These instructions are given by the programmer who is using compilers, interpreters, etc, to write programs. Examples of those languages are Basic, C++, Pascal, etc.
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 <iostream.h>
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 <iostream.h>
#include <stdio.h>
Documentul este oferit gratuit,
trebuie doar să te autentifici in contul tău.
