WELCOME TO QBASIC

Chapter 1: Introduction to BASIC

Programming

Have you ever, when seeing a game or another program, asked yourself : How did they do that? 

Every program, every game you run on your computer, has been written by someone using a special software development tool called a programming language.

By definition:    A program is a set of instructions that makes the computer work.  The instructions constitute of keywords, sometimes called reserved words, that have special functions such as:

• Clearing the screen
• Writing data to the screen
• Getting user input
• Executing loops
• Changing colours
• Playing sounds
• Opening files
• Etc.

There are different programming languages. Some are difficult to use, understand, other are limited to special purposes such as scientific calculations, drawing or database management.

Some programming languages out there:

The Qbasic IDE

The Qbasic IDE

The Qbasic IDE is quite simple to understand. It is divided into two windows: the Untitled Window and the Immediate window.
You should type your instructions in the untitled window.
To run your program, click on  Run -> Start  or  Press F5
To get out of Qbasic, click on  File -> Exit.
We'll see more about the Qbasic IDE later.

Two BASIC reserved words

It is not necessary for you to know all the BASIC reserved words to get started. You could write a lot of  programs using about 10 keywords. To get started we'll be using only two of them:

CLS	This statement is used to clear the screen.
PRINT	The PRINT statement is used to display data on the screen.

Your First BASIC program

To begin we will write a simple program that will output a text on the screen.
Type the following in the untitled window:

PRINT "Hello!" PRINT "This is my first BASIC program."

To run your program:

Click on Run � Start or Press the function key F5

The output on the screen will be as follows:

Hello! This is my first program. Press any key to continue

Once the execution of your program is completed, BASIC will display a "Press any key to continue" message on the screen. So press any key to return to your programming environment.
If you run your program many times, you will notice that the same text will be displayed several times on the screen as shown below:

Hello! This is my first program. Hello! This is my first program. Hello! This is my first program. Hello! This is my first program. Press any key to continue

To get your screen cleared each time you run you program, put the CLS statement at the beginning of your program:

CLS PRINT "Hello!" PRINT "This is my first BASIC program."

Note the presence of inverted commas(" ") in the PRINT statement. Always put inverted commas if you want to output sentences or characters.

Mathematics symbols

Some mathematical operators and their BASIC equivalent:

Operation	Mathematics	BASIC equivalent
Plus	+	+
Minus	-	-
Multiply	x	*
Divide	�	/
Exponential	a2	a^2

 

Storing data in the computer memory
Data types: Constants and Variables

You may need to store data in the computer when writing your program.
Data is classified into 2 types:

• Numbers
• Character Strings

Example of numbers:

10    +5    0.32    -1.234

Examples of character strings:

"Hello! how are you?"   "John Smith"   "14 Royal Road"   "$123"

Characters consist of letters, numbers, symbols and special characters.
To store data in the memory you will need to put them first in memory variables or constants.
A memory variable will store values that vary, change.
A memory constant will store values that remain constant (i.e. they don't change).

The Computer Memory

The memory of the human being contains millions of cells that store the different information that you have acquired in your life. Similarly the computer memory could be represented as storage cells. Each cell can be given a name or an address as follows:

Value	10	+5	0.32	-1.234
name of cell	a	b	c	d

Value	Hello! How are you	John Smith	14 Royal Road	$123
name of cell	a$	b$	c$	d$

Declaring variables

BASIC has received many critics because of its ability of creating & declaring variables on the fly. Qbasic allow you to declare variables.
The DIM statement is used to specify a data type for a variable. Variables declared should not end with a suffix.
The syntax is as follows:
DIM variable AS type
Example:
 

DIM userrname AS STRING DIM age AS INTEGER username = "John Smith" age = 23

The code above is equivalent to

username$ = "John Smith" age% = 23

So what method of working with variables is better?
Personally, though you might encounter both ways in the tutorial, I prefer to use the first one. It's a good habit to declare every variable you use.