QBASIC Lesson 1 - An introduction

BASIC as a language has been around for a long time, and has seen many
different versions and variations. Microsoft QBASIC is quite a good version;
it has a very good range of features and can support virtually anything that
a beginner could want to do, albeit slowly. Learning it will be a useful step
on the road to becoming a proficient programmer.

Before we delve into the language itself, it is important that you understand
the basics of the QBASIC editor. The main window, the editing window, is where
you type your program. Pressing Shift+F5 will run this program, or you can
select run from the Run menu. There is a small window at the bottom of the
screen called the immediate window, where anything that you type will be
immediately run. Along the top menu are some useful menu icons, most useful
of all will be "help" - this contains information on how to use the editor
and also an index of commands which is immensly useful, although some of
the definitions can be a bit cryptic. Feel free to explore through the help
files, there is a lot of useful information.

Okay, I think it's about time for our first program. At this point, by the
way, it will be very useful to have this tutorial open in one window and
QBASIC open in another. If not, you're going to spend a lot of time switching
between the two.

Okay, click at the top of the editing window so that the cursor appears and
you can type in words. Put CAPSLOCK off - you'll find out why later, but trust
me, it is important. Now, enter:
print "Hello World!" 
and press return. You will notice that the word 'print' instantly changes 
from lower case to upper case - this is the computer's way of showing that
this is a command that it understands.

Any guesses at what this program will do? Press Shift+F5 to find out.
Original or what? Okay, so it may not be Doom, but it's a program. Press any
key to get back to your editor, and have a quick think about what happened.
The computer starts at the top of the file and works down. The first thing
it comes to is "PRINT", which means "Place on the screen the following:". It
then comes to the string (string means stored text) "Hello World", takes this 
as per instruction and prints it out on the screen. Easy.

You may be thinking that a program that prints "Hello World" every time you
run it is a bit useless, and you'd be right. A computer is supposed to do
things that would be difficult for a person to do, and you could do exactly
the same thing with a piece of paper and a pen. That's where variables and
strings come in.

Variables are the most important thing that a computer deals with. A variable
is simply a stored number that can be printed, added, subtracted, multiplied,
drawn, in fact anything at all that you do on a computer involves variables.
When you are playing Doom 2, your health is stored in a variable. Whenever
you are hit, a command decreases the variable. When you are playing Quake,
you position is stored in variables. Whenever you move, these variables are
changes.

So how do we use variables in QBAISC? Easy. Simply type in any word that the
computer doesn't understand (not in speech marks though, otherwise it will
be treated as text) and it will treat it as a variable. Here is an example:
cabbages=1
cabbages=cabbages+1
Most programmers, however, don't like the idea of using massively long
variable names, mainly because it takes ages to type in.

Okay, big shock now: we're going to write a useful program. Not a stunningly
useful program, I admit, but a useful one. We're going to write a program
to ask you for two numbers and print out the result of multiplying the
two together. I think the best way of doing it is to give you the program
so that you can type it in and see that it works, then I'll go through it a
line at a time:
cls
input "Please enter the first number",a
input "Please enter the second number",b
r=a*b
print "The answer is";r

Okay, now here's the line-by-line breakdown:

cls
This is a very useful command that is also very easy to use - just put it
in and it CLears the Screen.

input "Please enter the first number",a
The input command is used to let the user type in letters or numbers. In this
case it's asking for a number, which will be placed in the variable a. So,
it will print "Please enter the first number? ", wait for you to type a
number then put this number in the variable a.

input "Please enter the second number",b
This input command works in the same way, but it prints a different message
and the number that you type ends up in b.

r=a*b
This is the command that does the work. It makes r equal a time b, in other
words: work out what a*b is and put it in a.

print "The answer is";r
This is an interesting one. You see, the print command can also print out
variables, and using this command is equivalent to saying: Put "The answer is"
on the screen followed immediately by the value of r. The semicolon tells
the computer not to go onto the next line before printing the value of r;
try it with no semicolon, or with a comma there instead. It will look
different each time.

That should about wrap it up for this tutorial. Experiment with the different
programs and commands; there is nothing that you can do that will damage your
computer. Look in the index of commands for further information on any of
the commands I have talked about. I'll leave you to it.