Scan&OCR: gafz, 2006
DOING THINGS IN ORDER
IMMEDIATE MODE AND KEYWORDS
OPERATORS AND EXPRESSIONS
SETTING OUT TEXT
THE FUNCTION KEYS
FUNCTION KEY OPERATIONS
HANDLING PROGRAMS ON CASSETTE
STORING LARGER AMOUNTS OF INFORMATION
THE CHARACTER SET
SOUND 'N' RHYTHM
MAKING PROGRAMS OUT OF PROBLEMS
MINIMAL BASIC FEATURES
USING MACHINE CODE
RULES OF BASIC
COMMANDS AND STATEMENTS
MACHINE OPTIONS (GENERAL)
BUILT-IN FUNCTIONS AND VARIABLES
Let's begin by using the machine. That way you can get used to it and see demonstrations of its abilities. Technicalities will be explained later.
It is best if you follow this part of the manual in sequential order, because it is designed to help you to get acquainted with your new computer. Wherever there is scope for you to follow up one subject before you go on to look at others, cross references are provided, so you can learn about the machine in whatever order and at whatever speed you feel comfortable. The second part covers each 'section' of programming (they all link up in reality as you will see) in detail and on a slightly higher level than in the first part. The Reference Section at the end will help you to discover more about the Enterprise once you have learned the fundamentals of controlling the computer.
Before you look at some programs, experiment with the keyboard a bit. You can type whatever you like and it won't hurt the computer at all. If the computer stops producing letters in response to your typing, just press the 'reset' button at the back. The joystick is really good to mess about with-and you'll see how handy it is later on. In the meantime let yourself get to know the computer. It's got a lot to offer you.
Note: When you are just using the computer for word processing (see pages 38-42 and the tables on pages 36 and 37), you don't need to insert the IS-BASIC cartridge. In order to write BASIC programs, however, you need to have this cartridge plugged into the ROM BAY on the left-hand side of the machine.
Try typing in the contents of the box below. Computers are a bit funny about little mistakes, so check your typing before you finish. Remember that you must press the key marked 'enter' at the end of each line. Don't forget the numbers which begin the lines, they're important too. However, you needn't worry about the blank spaces which appear after the numbers. The Enterprise can put spaces in automatically, to make programs look neater. Notice that computers use a special symbol for nought (0), to distinguish it from the capital letter O.
110 PLOT 640, 360,
140 FOR RADIUS= 250 TO 1 STEP - 16
150 SET INK RND (3) + 1
160 PLOT ELLIPSE RADIUS, RADIUS,
170 PLOT PAINT
180 NEXT RADIUS
If you make a typing error, it is easy enough to correct it. If you're still on the same line as the mistake, pressing the key marked 'erase' will move the red flashing 'cursor' to the left, removing letters etc. as it goes. If you have to go back to a previous line, use the joystick to place the cursor at the end of that line, then erase back as far as your error. You can now type the correction, finish off the line by pressing 'enter', and move the cursor (using the joystick) to the bottom of the screen again, or wherever else you want it. Remember that whenever you press a key, the place where your letter or number will appear is the place where the cursor is located at that particular moment.
Later, in the chapter on 'Editing Programs' (page 33), we shall discuss some more versatile ways of making changes.
When you've typed in the program, type the word RUN and press 'enter' again. Alternatively, you can press the key marked 'function 1', above the number keys. If you use this key, you will not need to press 'enter', and it's quicker than typing RUN. (For more about 'function' keys, see page 43.) Then watch for a while. If you've made a mistake, the computer will print 'Not understood' (or a similar message) on the TV screen. Don't worry at all if that happens. Press function key 5 and then function 2, to take another look at the program-then correct the problem, and try again.
Commands which this manual suggests you type into the computer will always appear on the page in capital letters. This is mainly for emphasis, but partly because the computer itself often displays BASIC commands in capitals. However, you can type words like RUN (and other BASIC commands) in small letters as well; the computer will understand you perfectly. You don't need to go to the trouble of pressing the 'shift' key to get from small letters into capitals all the time.
Any words you don't understand can be found in the Glossary, pages 209-221.
To stop the program, press 'stop'. You will see the response
STOP AT LINE--- (--- is a number)
WHAT'S A PROGRAM?
A program is a set of instructions which tells the computer what to do. There's nothing special or magic about that, but a computer can't do anything at all without a program. Programs are very exact and very detailed, but then so is embroidery. And, just like any other skilled pastime, programming can be done seriously, or just for fun.
If you want to, you can re-start the program by typing in CONTINUE and pressing 'enter'. Even better, press the key marked 'shift' and at the same time press the function key numbered 1 (you used this to RUN the program). The program will then resume from the point at which you stopped it.
On the other hand, if you're bored with this you can add to it. Type in the line below.
135 SET PALETTE RND (256), RND (256), RND (256), RND (256)
Having run this program and stopped it, you will now be left with a picture filling the screen. This doesn't make it very easy for you to read what you're typing in. To tidy up the screen, type TEXT, press 'enter' and the screen will be returned to the full text display. Again, if you want to save time (and effort), press function key 5.
This time, when you have finished typing in the new line, type LIST. Function key 2 will also do this. By now you should be able to remember to press enter' whenever you have finished typing in an instruction or a program line. 'Enter' is the key which tells the computer to do what you have typed. Usually, until you press it, nothing will happen; however, you don't normally need to press 'enter' with the function keys-as you have probably found out.
LIST is a word which will show you the whole of a program on the screen (or as much of it as you can fit on the TV screen at one time). You can see now that your new line has fitted in with the old ones. The whole program is now in numerical order. This is the order in which the computer will carry out your instructions when the program is RUN.
GETTING RID OF
When you get fed up with a program, simply type NEW, press 'enter', and the program will be gone.
Using this computer you can produce all kinds of sounds and many colours very easily. But it is not just there to make noises and display rainbows. Your computer can draw very fine pictures, make decisions, do big calculations very rapidly, sort things into any order you like and repeat things as often as you want.
The programs on the following pages are simple examples of the Enterprise's talents.
Try them all! They are just a few things you can do with this machine. In this book you will find out how to do all of them for yourself-plus a lot more. Don't forget to use TEXT to get a full screen to type onto when you want it. You can also use CLEAR SCREEN to empty the TV screen when it gets full. These commands don't actually remove any program lines from the computer's memory; you can view the whole program again any time you like, by typing LIST.
10 PROGRAM "Fire-tunnel"
30 ! This program draws a
40 ! multi-coloured tunnel with
50 ! exploding fireballs.
100 GRAPHICS HIRES 256
110 LET X = 640: LET Y = 360
120 FOR R= 1 TO 255
130 SET INK R
140 LET A = X-R-220: LET A 1= Y-R-50
150 LET C=X+R+220: LET C1=Y+R+50
160 PLOT A, A1; A, C1; C, C1; C, A1; A, A1
170 PRINT R
190 FOR BALL= 1 TO 100
200 CALL FIREBALL (256, X, Y)
1000 DEF FIREBALL (COLOURS, A, B)
1010 SET LINE MODE 3
1020 SET INK RND (COLOURS)
1030 FOR GO= 1 TO 2
1040 FOR AROUND =1 TO 650 STEP 30
1050 PLOT A, B, ELLIPSE AROUND, AROUND
1080 SET LINE MODE 0
1090 END DEF
100 ! This program will draw boxes.
120 ! 100-140 are comment lines.
130 ! You don't have to type them.
140 ! -----------------------------
150 CLEAR SCREEN
160 PRINT AT 5,11: "THIS PROGRAM WILL"
170 PRINT AT 6,10: "DRAW BOXES FOR YOU."
180 PRINT AT 8,1: "The program will ask you to type in"
190 PRINT AT 9,1: "some numbers, in pairs. The first"
200 PRINT AT 10,1: "number of each pair should not be more"
210 PRINT AT 11,1: "than 1279, and the second should not"
220 PRINT AT 12,1: "be more than 719. Press ' enter' "
230 PRINT AT 13,1: "after typing each number."
240 FOR A= 1 TO 5000
250 NEXT A
260 ! -------------------------------
270 ! Lines 240-250 make the computer
280 ! wait for about 10 seconds.
290 ! -------------------------------
310 CLEAR SCREEN
320 INPUT AT 5,5, PROMPT "Numbers for one corner: ":X
330 INPUT AT 6, 29, PROMPT " '':Y
340 INPUT AT 8, 5, PROMPT "Numbers for opposite corner: ":V
350 INPUT AT 9,34, PROMPT " ":W
360 PRINT AT 11,5: "For how long should the box"
370 PRINT AT 12,5: "be displayed?"
380 INPUT AT 14,5, PROMPT "Seconds: ": TIME
390 ! -----------------------------
400 ! Lines 450-480 are the
410 ! instructions for drawing the
420 ! box and holding it on the
430 ! screen for the time you want.
440 ! -----------------------------
460 PLOT X,Y;X,W;V,W;V,Y;X,Y
470 FOR B =1 TO 500*TIME
480 NEXT B
500 PRINT AT 15,18: "More?"
520 INPUT AT 17,17, PROMPT "y or n:" :ANS$
530 LOOP WHILE ANS$ < > "y "AND ANS$ < > "n"
540 LOOP WHILE ANS$
! This is the end of the program.
100 ! This program sorts 10 numbers
106 ! into numerical order.
110 NUMERIC ARRAY( TO 10)
120 NUMERIC VAR,NUM,BIG
130 CLEAR SCREEN
150 PRINT AT 10,10: "NUMBER SORT"
160 FOR N= 1 TO 10
170 PRINT AT 14,10: "TYPE NUMBER";N;
180 INPUT PROMPT ": ":ARRAY(N)
190 PRINT AT 14,25:" "
200 NEXT N
210 CLEAR SCREEN
220 PRINT AT 20,20: "SORTING... "
240 LET FIN= 10
250 FOR X = 1 TO 10 255 LET BIG = 0
260 FOR Y= 1 TO FIN
270 IF ARRAY(Y)>BIG THEN LET BIG = ARRAY(Y)
280 IF ARRAY(Y) =BIG THEN LET NUM = Y
290 NEXT Y
300 LET VAR = ARRAY(FIN)
310 LET ARRAY(FIN) = BIG
320 LET ARRAY (NUM) =VAR
340 LET FIN= FIN -1
350 NEXT X
355 CLEAR SCREEN
360 FOR X= 1 TO 10
370 PRINT ARRAY(X)
380 NEXT X
100 ! This program gives the
110 ! area/circumference of circles.
130 LET A$ = " of the circle is: "
140 LET B$= "Type the radius of the circle: "
150 NUMERIC RADIUS,AREA,CIRCUM
170 CLEAR SCREEN
180 PRINT AT 10,10:"1) AREA"
190 PRINT AT 11,10:"2) CIRCUMFERENCE"
200 PRINT AT 12,10:"3) QUIT"
220 PRINT AT 15,10: "Type the number"
230 INPUT AT 16,10,PROMPT "of your choice: ":NUM
240 LOOP WHILE NUM < 1 OR NUM > 3 OR NUM < > INT(NUM)
250 CLEAR SCREEN
260 IF NUM =1 THEN
270 INPUT AT 10,1,PROMPT B$:RADIUS
280 LET AREA = PI*RADIUS^2
290 PRINT AT 15,5: "The area";A$;
300 PRINT AT 16, 4: AREA
310 FOR X =1 TO 5000
320 NEXT X
330 ELSE IF NUM = 2 THEN
340 INPUT AT 10, 1, PROMPT B$:RADIUS
350 LET CIRCUM = 2*PI*RADIUS
360 PRINT AT 15,1: "The circumference '';A$
370 PRINT AT 16,1:STR$ (CIRCUM)
380 FOR X = 1 TO 5000
390 NEXT X
400 END IF
410 LOOP WHILE NUM < > 3
Try altering the programs if you want to. It's not a good idea to change the spelling of program instructions, because the computer won't understand if you do. But where words appear between inverted commas you may change them without messing up the program itself. Numbers can also be changed. By doing this you may be able to work out what the program is doing-changing a number will often affect the number of times something is done, or the position of characters on the screen. Some numbers within programs are codes-that is, they stand for something else; a colour for instance. You will learn all you need to about these further on in the manual (try page 95 for colour and 104 for other codes if you like).
Remember always that whatever you type will do the computer no harm at all. The worst that can happen is that you will type in something the computer fails to understand. For example, in the number-sorting program (page 11), you might have typed:
250 FOR X= 1 TOO 10
In that case, after running the first part of the program, the computer would stop and the screen would show:
*** Not understood.
250 FOR X = 1 TOO 10
Error messages are explained in detail on pages 204-208.
If you get completely stuck and want to start again, press the 'reset' button at the back of the machine. This will put you back where you were when you switched the machine on, except that the computer will remember any program you have just typed in. This is best kept for emergencies, though. Normally you will use the 'stop' or 'hold' key for stopping a program that is running. When you use 'reset', you will have to type RUN again to make the program restart.
The 'hold' key is simply used to hold up the program and freeze the action at whatever point you have reached. This is handy if you want to look at a moving picture in a graphics display -or even if you just need a tea break in the middle of a difficult game of Space Invaders. To carry on with the program, simply press the same key again. Notice that 'hold' is very useful if you are LISTing a long program which disappears off the screen, and you want to halt the motion so as to examine some particular line.
The 'stop' key is used if a program is running and you want to halt it so as to modify (or erase) it, or to LIST and examine it before typing CONTINUE to make the program resume.
You've now had some fun with the machine and, hopefully, introduced yourself. You probably didn't see how some of the programs worked, so this is where we begin adding knowledge to enjoyment.
You've already learned in brief what a program is, but there is a little more to writing it than just giving instructions. You can think of a program as a way to solve a problem using a computer. A computer is either a tool which can expand and speed up your brain power, or it is a pleasurable thing to own on which you can play games or invent some for yourself.
All computers understand instructions, usually in the form of words or lists of numbers. We will be using words to communicate with the Enterprise. Each word is a small instruction; you can put them together like a puzzle or a story to make up bigger instructions and, eventually, complete tasks. That is what programming is essentially about. Giving the computer instructions - in the order in which you want them to happen.
The diagram below shows (using an everyday example) how one task must be broken up into several small ones to make up a program.
Now you know what a program is, let's move on a stage further. Just as there are many different ways to talk to another person, so there are many ways to program a computer. And in the same way that there are human languages, there are computer languages.
Languages are made up with definite limits and types of task in mind. Some are especially for programs involving long lists of things, others are particularly good at making pictures with a computer. Others still are there to teach people how to program.
The language you are learning through this manual is known as BASIC. It uses words with similar spelling and meaning to English words. It is therefore very easy to learn and understand, even if you are inexperienced with computers. All the programs in this manual are in BASIC, and it is the language the computer understands as long as the IS-BASIC cartridge is plugged in. Remember that, from now on, all the instructions and all the information in this manual relate to BASIC. Some other languages are totally different in both philosophy and approach, and they usually look completely different from BASIC.
Look at this:
10 PRINT "Hello!"
You will know by now that it's a program line-it's one small task which could make up part of a bigger one.
Just as, in a story, each sentence tells you something, so each line in a program tells the computer to do something. If you want to tell the computer to carry out a task, you will need several lines to do it.
DOING THINGS IN ORDER