C# Programming Yellow Book

Computers and Programs

In this chapter you are going to find out what a computer is and get an understanding of the way that a computer program tells the computer what to do. You will discover what you should do when starting to write a program, to ensure that you achieve a “happy ending” for you and your customer. Finally, you will take a look at programming in general and the C# language in particular.

Computers

Before we consider programming, we are going to consider computers. This is an important thing to do, because it sets the context in which all the issues of programming itself are placed.

An Introduction to Computers

A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs.

One way of describing a computer is as an electric box which hums. This, while technically correct, can lead to significant amounts of confusion, particularly amongst those who then try to program a fridge. A better way is to describe it as: A device which processes information according to instructions it has been given.

This general definition rules out fridges but is not exhaustive. However, for our purposes it will do. The instructions you give to the computer are often called a program. The business of using a computer is often called programming. This is not what most people do with computers. Most people do not write programs. They use programs written by other people. We must therefore make a distinction between users and programmers. A user has a job which he or she finds easier to do on a computer running the appropriate program. A programmer has a masochistic desire to tinker with the innards of the machine. One of the golden rules is that you never write your own program if there is already one available, i.e. a keen desire to process words with a computer should not result in you writing a word processor!

However, because you will often want to do things with computers which have not been done before, and further because there are people willing to pay you to do it, we are going to learn how to program as well as use a computer.

Before we can look at the fun packed business of programming though it is worth looking at some computer terminology:

Hardware and Software

If you ever buy a computer, you are not just getting a box which hums. The box, to be useful, must also have sufficient built-in intelligence to understand simple commands to do things. At this point we must draw a distinction between the software of a computer system and the hardware.

Hardware is the physical side of the system. Essentially if you can kick it, and it stops working when immersed in a bucket of water, it is hardware. Hardware is the impressive pile of lights and switches in the corner that the salesman sold you.

Software is what makes the machine tick. If a computer has a soul, it keeps it in its software. Software uses the physical ability of the hardware, which can run programs, to do something useful. It is called software because it has no physical existence and it is comparatively easy to change. Software is the voice which says “Computer Running” in a Star Trek film.

All computers are sold with some software. Without it they would just be a novel and highly expensive heating system. The software which comes with a computer is often called its Operating System. The Operating System makes the machine usable. It looks after all the information held on the computer and provides lots of commands to allow you to manage things. It also lets you run programs, ones you have written and ones from other people. You will have to learn to talk to an operating system so that you can create your C# programs and get them to go.