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The Project 64 etext for Commodore BASIC articles #1, converted by
anonymous.  This etext was created by concatenating several documents
into one.  All of the included documents were retrieved from the
Headgap BBS, sysop Bob Nunn, telnet://bbs.headgap.com:1474,
login: guest, password: guest.

Basic Language (11 - Basic Language).
Introductory Basic Lesson (13 - Begin Basic 1).
Basic (14 - Begin Basic 2).

BASIC110.TXT, July 1996, etext #63.

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The Project 64 etext of Basic Language (11 - Basic Language).

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 BASIC LANGUAGE
 AUTHOR: UNKNOWN
 FROM: CLARKSVILLE COMMODORE USERS GROUP

BASIC (Beginners All-purpose Symbolic Instructional Code) was
developed in 1963 by John G. Kemeny and Thomas E. Kurtz at Dartmouth
University for use with a time-sharing computer system developed by
General Electric. BASIC is the most used computer language. At one
time BASIC was the first Computer language taught in Computer Science
classes because of its relative simplicity and similarity to plain
English.

BASIC is a High Level computer language, that is, it is a language
that is people oriented rather than a machine oriented language (i.e.
Machine Language). BASIC as used on the C-64 is an Interpreted
language, each Command in BASIC calls upon one or more built in
Machine Language routines during execution. Interpreted languages are
much slower in execution than Machine language because of this. BASIC
can be Compiled using a special program called a Compiler. A Compiler
scans the BASIC language program, converts it to Machine Code and
re-writes the program back to the mass storage device in compiled
form. A Compiled Program can RUN on the order of 100 times faster than
the Interpreted version. The original BASIC Program is called the
Source Code and the Compiled version is the Object Code.

Now-a-days BASIC has fallen from favor with Colleges and PASCAL is
generally taught as the first Computer language. PASCAL is a highly
structured language, that is, the structure of the program is very
rigid. EXAMPLE: All Variable names and Variable types that are going
to be used in the program must be declared at the beginning of the
program:

    VAR
     EMPLNO: INTEGER;
     HOURS,RATE: REAL;
     P,Q: BOOLEAN;
     C: CHAR;

other parts of the PASCAL program are equally rigid in structure. One
of the reasons to teach PASCAL rather than BASIC is because computer
programming is a highly logical occupation and rigidly structured
languages force the programmer to think through the problem carefully
before writing the program.

Also the structure of the program makes it self-documenting.
Microsoft BASIC (Version 2.0) the language used by the C-64 contains
over 70 different Commands. The possible number of ways of combining
these Commands is so large that my computer cannot calculate it. One
of the things to take into account when writing a computer program is
whether to make it transportable or not. Consider the simple task of
clearing the screen, you can clear it by typing:

   10 PRINT "Reverse Video Heart"

If you use this method and later want to make your program RUN on a
different manufacturers computer it will have to be changed.  You can
also Clear the Screen by typing:

   10 PRINT CHR$(147)

If you use this method this line will run on any manufacturers
computer.

To make your programs more transportable use the ASCII CHAR$ for
control functions where possible and avoid using PEEKS and POKES
(because the addresses are different on different machines).

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End of Basic Language (11 - Basic Language).

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The Project 64 etext of an Introductory Basic Lesson (13 - Begin
Basic 1).

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Introductory Basic Lesson

Commands vs. Statements: BASIC makes a distinction between what are
know as commands and statements. The PRINT statement tells the
computer to display information in the screen for us to look at. So
what's a command? We use commands to tell BASIC directly that we want
it to do so mething for us.  Normally, commands are typed in directly,
although it is possible for them to be used in programs. We just type
in the command and BASIC goes and executes it. We dont use line
numbers, as we would for statements in a program. Here are some of the
most important commands that you will need to know to effectively
write programs in BASIC:

  LIST
  RUN
  SAVE
  LOAD
  NEW

LIST: When we want to look at a program that we have typed in,
especially a large one, we use the LIST command. By typing LIST, we
are telling BASIC that we want to see our program, to have it LISTed
for us. BASIC responds by displaying the whole program on the screen,
starting with the lowest line number and displaying lines in ascending
order until the end of the program is reached If the program is large,
it may scroll off the top of the screen as it is being listed. Type in
this short program, which we will use to demonstrate how commands
work.

 10 PRINT "THIS PROGRAM WILL BE USED"
 20 PRINT "TO DEMONSTRATE BASIC COMMANDS"
 30 PRINT "IMPORTANT BASIC COMMANDS ARE"
 40 PRINT "LIST"
 50 PRINT "RUN"
 60 PRINT "SAVE"
 70 PRINT "LOAD"
 80 PRINT "NEW"
 90 END

Be sure to hit the return key after each line that you enter. Now type
LIST. The program that you just typed in is displayed on the screen.
You can LIST an entire program, or only part of it. You can list
individual lines, if you want. Try LIST 20. Line 20 will be LISTED.
You can also LIST a range of lines by using the hyphen (-).  Try this:
LIST 20-60. Line 20-60 will be LISTED. You can LIST a program up to a
certain point from the beginning.  Try LIST -70. The program, up to
line 70, is displayed. Finally, you can LIST a program from a certain
point to the end. Try LIST 30-. What happens? Do you see how LIST
helps you look at all or part of your program?

RUN: RUN is the command that you give BASIC when you want your program
to be translated into action by the computer, or to be EXECUTED. When
BASIC executes your pr ogram, it starts with the lowest line number,
and carries out the instuctions it finds on each line, in ascending
order, until it reaches the END statement. What do you think the
program you typed in will do when you type RUN? Type RUN ,and see if
you were right. The program should have printed the following on the
screen.

THIS PROGRAM WILL BE USED TO DEMONSTRATE BASIC COMMANDS IMPORTANT
BASIC COMMANDS ARE:

  LIST
  RUN
  SAVE
  LOAD
  NEW

SAVE: After we have typed in a program we usually would like to save
our work; otherwise, we'd have to type in the program in again every
time we wanted to use it. Fortunately, there are magnetic disks that
we have to save pro grams on. When you save a program, you have to
give it a name so that you can refer to it later if you want to use
it. The name, or FILENAME, can be almost any combination of letters
and characters, but it's a good idea to use a name that makes sense to
you so you can more easily remember what the program is used for. You
would use the SAVE statement like this: SAVE "filename",8. You
substitute, where it says 'filename', the name for the prog ram that
you have chosen. The name must appear in double quotes , as indicated.
The comma and the 8 are used to tell BASIC t hat you want to save this
program to disk (BASIC associates the DEVICE NUMBER 8 with your disk
drive).  For example, if you choose DEMO for a name, you would SAVE
the program like this: SAVE "DEMO",8 Make sure that you have a
formatted disk in your disk drive and the program will be saved.

LOAD: LOAD is the exact opposite of SAVE. When we want to work on a
program that we have previously saved to disk, we have to LOAD it into
the computer.  The comm and looks like this: LOAD "filename",8. To
load the program that we just saved, assuming that it was named DEMO,
we would type: LOAD "DEMO",8. The program will be loaded into memory
for us to RUN, LIST, or edit. You have to use the exact name to load a
program that you used to save it or else the the computer will not
know what file you are looking for and respond with FILE NOT FOUND
ERROR.

NEW: What if you're done with a program and want to start working on a
new one.  This is where the NEW command comes in.  It tells BASIC that
you want to start work on a new program and to clear things out so you
can start from scratch. Make sure that you have saved the example
program, and now type NEW.  Now try to LIST the program. What happens?
Try RUNning it? What happens now? As you can see, BASIC has thrown out
your program and doesn't know anything about it anymore. You can now
start working on a new program, or you can bring back the old one, by
LOADing it. Be sure to be very careful with the NEW command, or you
might lose some work after working on it for a long time!

Line Numbers: You may have wondered how you would get rid of a program
line that you didn't want in the program anymore. With BASIC, deleting
lines is very easy. All you have to do is type the line number that
you want to delete and hit the RETURN key. The requested line will be
deleted. If you have the sample progam saved, type 20 and hit RETURN.
Now try listing the program.  Line 20 should have been deleted from
the program.

That will wrap up this lesson. Try practicing these commands until you
are confortable with them.

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End of an Introductory Basic Lesson (13 - Begin Basic 1).

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The Project 64 etext of Basic (14 - Begin Basic 2).

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BASIC

BASIC is an high level language that can be used to solve a problem or
perform some function on a computer. We can think of a program that we
write in BASIC as a set of instructions for the computer to follow to
perform some task Usually, a program will require some sort of data to
operate on. It will then process the data as we have specified, and
finally it will provide us with the result of that processing.

The data that we give to a BASIC program is called INPUT. The answer
that that we get back is called OUTPUT. As the program executes, the
computer uses memory to store and retrieve data. In any high level
language, there must be some convenient means for the program to
retrieve, store, and process data easily.

NUMBERS AND LITERALS: We've seen how the PRINT statement works, and
how we can use our computer like a calculator:

 PRINT 5
 PRINT 43 + 12
 PRINT "HELLO THERE"

Numbers, like 5, 43, 12, and literals, like "HELLO THERE", are what
are known as CONSTANTS. Their value never changes.

VARIABLES: A variable is a symbol used to represent a number or a
character string. As the name implies, a variable can be changed by
the programmer at any time. A variable is given a name, and through
this name, we refer to some number or character string stored in
memory.

ASSIGNMENT STATEMENTS: A variable is assigned a value through what is
know as an assignment statement. The LET statement lets us accomplish
this:

 10 LET X=1
 20 PRINT X
 30 END

In this program, the variable X is given the value 1, and is then
printed.  The value of a variable can be changed at will:

 10 LET X=1:LET X=2
 20 PRINT X
 30 END

In this program, the variable X is fi rst assigned the value 1, and
then is reassigned the value 2. When the program is RUN, the value 2
will be printed. The Statement LET is optional, and X=1, and LET X=1
do exactly the same thing:

 10 X=1
 20 PRINTX
 30 END

VARIABLE NAMES: You must follow these rules when giving names to
variables:

1) The first character must be a letter.

2) The second character is optional, a letter or a number.

3) Only the first 2 characters in the variable name are significant.
Names can be longer than 2 characters, but BASIC' sees' only the first
2 Characters. The names RATE RAT RA are all seen by BASIC as the
variable RA.

4) The third character may be % if the variable is to be used to take
on integer (whole number) values, or $, if the variable is to be used
for character string val ues, like "OUR HOUSE", or "COMMODORE",
EXAMPLES:

 A=5.3             numeric variable
 A%=5              integer variable
 A$="HELLO THERE"  character variable

Here are some examples of valid variable names:

 A      X1       B4        CC
 J$     K%       K3        NN$

Variables may be used in mathematical expressions or character string
manipulations. Let's write a short program to add 2 numbers and print
out the answer:

 10 A=7
 20 B=3.5
 30 C=A+B
 40 PRINT C
 50 END

THE INPUT STATEMENT: How do we get data to our program to process?
This is accomplished by using the INPUT statement. When a program
encounters this statement, it stops, and waits for the user to enter
some input data. The user will be prompted with a ? symbol, and may
then enter the data, terminated by pressing the RETURN key. Here's a
simple example of a program to take a number from the user and print
it out.

 10 INPUT A
 20 PRINT "YOU ENTERED THE NUMBER ";A
 30 END

The program should always prompt the user for the kind of input
required.  This can be done with a PRINT statement or the INPUT
statement itself.

 10 PRINT "ENTER A NUMBER"
 20 INPUT A
 30 PRINT "YOU ENTERED THE NUMBER ";A
 40 END

or:

 10 INPUT "ENTER A NUMBER";A
 20 PRINT "YOU ENTERED THE NUMBER ";A
 30 END

Let's write a program to take 2 number from the user, add them
together, and print out the answer.

 10 PRINT "ENTER THE FIRST NUMBER"
 20 INPUT A
 30 PRINT "ENTER THE SECOND NUMBER"
 40 INPUT B
 50 C=A+B
 60 PRINT "THE SUM IS ";C
 70 END

INPUT can be used to enter more than one value at a time.

 10 PRINT "ENTER THE 2 NUMBERS SEPARATED BY A COMMA"
 20 INPUT A,B
 30 C=A+B
 40 PRINT C
 50 END

Try experimenting with variables, and the INPUT statement. Have Fun!

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End of Basic (14 - Begin Basic 2).

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The end of the Project 64 etext for Commodore BASIC #1.

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