PX-BASIC

1. What it is

PX-BASIC turns the PX-42F into a small computer you program in BASIC, the language of the first home computers. It follows Palo Alto Tiny BASIC, from 1976: numbered lines, PRINT, INPUT, IF, GOTO, GOSUB, FOR. To that it adds the calculator itself:

• Its numbers. 34-digit decimals, from the library Plus42 computes with. 0.1+0.2 is exactly 0.3, and SIN, LOG and SQR have the calculator's precision.
• Its screen, keys and speaker. Lines and points, the keys as input, the calculator's tones.
• Its drive. Programs are saved as text files that a computer can open too.

2. Getting started

Installing

1. Make sure the calculator's firmware is the PX-42F-Plus with app API version 3 or later.
2. On the calculator, open Settings → USB Drive → Connect to Computer.
3. Copy BASIC.bin into BIN/APPS on the drive named PX-42F. From the project folder, make install does it.
4. Optionally, copy the example programs (.BAS files, in the project's sim/drive/BIN/APPS/BASIC/) into BIN/APPS/BASIC on the drive.
5. Eject the drive and press EXIT on the calculator.

Starting and leaving

Start it from Settings → Games & Apps → Apps → BASIC. It shows how much room there is for a program, then the prompt, >.

To leave, press ON at the prompt. The status bar asks LEAVE BASIC? ENTER=YES: ENTER (or ON again) goes back to the list of apps, and any other key stays in BASIC. Held for 2 seconds, ON turns the calculator off without asking, and the Sleep Timer does too.

The program you were working on is saved when you leave, as AUTOSAVE.BAS, and comes back the next time you start BASIC.

Your first program

BASIC keeps lines that start with a number, in number order, as the program. A line without a number runs at once. Type these three lines, pressing ENTER after each. Use the keyword map (SHIFT ▼, below) for FOR, PRINT and NEXT, and SHIFT before a key for one digit or symbol, or SHIFT ENTER (ALPHA) twice for NUM:

10 FOR I=1 TO 5
20 PRINT I,SQR(I)
30 NEXT

Then type RUN (or choose it from the keyword map): it prints each number and its square root. LIST shows the program again.

3. Typing

The status bar

The top right of the screen says what the keys do. The prompt, Edit mode and the GTO prompt all show the mode there:

ABC and abc: letters

The letters are where the calculator's ALPHA keyboard has them, as on the DM42: A to F on the top row, G to L on the second, M N O next to ENTER, then P to Z, row by row. = is after Z, and the bottom row types : . ? and a space.

NUM: digits and symbols

The digits and + − × ÷ are where they're printed (* and / for times and divide), with . and a space on the bottom row. The top rows type BASIC's symbols. E, on the calculator's E key, writes a number's exponent: 2E-3.

The other keys

The keyword map

Typing RETURN letter by letter takes six keys. SHIFT ▼ shows a map of BASIC's words laid over the keys: press a key to type its word, with the space or ( after it. The words are in eight pages by kind, and in alphabetical order on each page, reading along the rows. ▼ shows the next page and ▲ the one before (the page number is in the top right corner); the pages go round, so ▼ on the last page shows the first, and ▲ on the first shows the last. ON (shown as BACK), or a key with no word on it (an empty box), goes back without typing anything.

SHIFT R/S runs the program without the map.

Typing from a computer

With the calculator connected by USB, open its console port ("PX-42F Console") in any terminal program; the speed setting doesn't matter. A Mac lists it with ls /dev/cu.usbmodem* (the first of two); screen /dev/cu.usbmodem2101 opens it. Then:

• What you type there goes to BASIC as if typed on the keys, in any case: lowercase becomes uppercase, except inside quotes.
• Paste a whole program: each line goes in as typed.
• Everything the screen shows also goes to the terminal, so a long listing can be read there.
• Ctrl-C stops a running program, as R/S does; at the prompt it clears the line.
• The arrow keys work as you'd expect: ← → move in the line, Home and End go to its ends, Delete deletes under the cursor, ↑ ↓ step through the history. Ctrl-A Ctrl-E Ctrl-B Ctrl-F Ctrl-P Ctrl-N and Ctrl-U do the same, for terminals that don't send the arrows.
• TAB completes the keyword being typed, as in a Linux shell: PR TAB gives PRINT , SQ TAB gives SQR(. When several words fit, it goes as far as they agree (STO becomes STOP); when that adds nothing, it lists them. Not inside quotes. A TAB inside a pasted program is a space.
• Editing the middle of a line redraws it with ANSI codes (carriage return, clear to the end of the line, cursor back): any ordinary terminal handles them. If CoolTerm shows odd characters or never sends the arrows or Ctrl-C, set it to Raw Mode (Connection → Options → Terminal), which sends each key at once.

4. Writing a program

• A line with a number (1 to 32767) goes into the program. Lines are kept in number order, whatever order they're typed in. Number them in tens (10, 20, 30) to leave room for lines in between.
• The same number again replaces that line. The number alone deletes it.
• A line without a number runs at once: PRINT 2^64, or RUN.
• Several statements fit on one line, with : between them: 10 X=1:Y=2:PRINT X+Y.
• A line holds up to 80 characters, more than the screen's 31: the text wraps.

Editing the program

You don't have to retype a line to change it. On the calculator, ▼ at an empty prompt or SHIFT ▲ at any prompt opens List mode. It works in two steps, on one screen:

1. List mode. The program is shown a line to a row, the current line highlighted, and the header says LIST. It opens on the line you last entered, or on the first line. ▲ and ▼ move the highlight, and the list scrolls; SHIFT with them moves a screenful. The list goes round: ▲ on the first line goes to the last, and ▼ on the last goes to the first. To go to a line, press SHIFT GTO (SHIFT XEQ), its number and ENTER. With no line of that number you get the nearest one, and of two as near the earlier one. ← deletes a digit, and EXIT cancels. SHIFT ← deletes the highlighted line: the header asks DELETE 20? ENTER=YES, ENTER deletes it and any other key keeps it. ENTER edits the highlighted line. EXIT (the ON key) goes back to the prompt.
2. Edit mode. The line is edited where it is, in the list: all of its text, as many rows as it needs, with the rest of the program still shown around it. The header says EDIT and what the keys do, with the mode at the right. ▲ moves the cursor left and ▼ right (the cursor is the white block). What you type goes in at the cursor; ← deletes the character before it; SHIFT ← clears the line; SHIFT ▼ is the keyword map; SHIFT ENTER goes to the next mode (the header then shows [a], or [#]).
   • ENTER accepts the change: the line replaces the old one.
   • EXIT cancels: the line stays as it was.
   Either way you're back in List mode, on the same line, to move to another one.

• A new line from an old one: change the number while editing. The edited line goes in under the new number, and the old line stays.
• Deleting a line: edit it down to just its number and press ENTER. The line is removed, and the highlight moves to its neighbour.
• A line with no number (the number edited away) is dropped as if discarded: it would run as a command, which isn't what you meant.

At the prompt, ▲ brings back the last commands, for running them again, as the terminal’s up arrow does. To change one first, press ← or type something: from then on the arrows move the cursor. At a program's INPUT, ▲ and ▼ only move in what you've typed.

5. Numbers

Every number is a decimal of up to 34 significant digits, from ±10⁻⁶¹⁴³ to ±10⁶¹⁴⁴, the same numbers Plus42 computes with. Because they're decimal, the sums that go wrong in most computer languages come out right: 0.1+0.2 is exactly 0.3. A fraction with no exact decimal still rounds, as on any calculator: 1/3 is 0.333…3, 34 threes.

How PRINT shows them

• Rounded to 12 significant digits, like the HP-42S's display. DIGITS n changes that, from 1 to 34. After DIGITS 34, PRINT SQR(2) shows 1.414213562373095048801688724209698.
• No zeros at the end: 2.50 prints as 2.5.
• With E when the number is too large for the digits, or below 0.000001: 1.5E-7, 6.02214076E23.
• The number is kept to all 34 digits; DIGITS only changes how it's shown.

Writing them

12, -3.5, .25, 2E-3, 6.02214076E23. An E is the exponent only with digits after it, so 2*E is two times the variable E.

Variables and the array

• Variables: 26, A to Z, one letter each. They start at 0, and RUN sets them to 0.
• The array: @(0) to @(1023), for lists and tables: @(I)=I*I.
• Your own arrays: DIM makes lists and tables with one or two indices, named by a letter: DIM A(10), DIM M(5,5). See Arrays below.

6. Expressions and functions

Arrays: DIM

DIM A(n) makes a list of numbers, A(0) to A(n). DIM M(r,c) makes a table: M(0,0) to M(r,c), so DIM M(2,3) has 3 rows of 4. DIM S$(n) makes a list of strings, S$(0) to S$(n). Several can be made in one statement: DIM A(9), M(4,4), N$(20).

10 DIM M(2,2), N$(2)
20 FOR I=0 TO 2:FOR J=0 TO 2
30 M(I,J)=I*3+J
40 NEXT J:NEXT I
50 N$(0)="ONE":N$(1)="TWO"
60 PRINT M(1,2);" ";N$(1)

• An element is used like a variable: in expressions (A(I)*2), on the left of =, in INPUT A(I,J) and INPUT S$(I). The index can be any expression, A(A(1)+1) too.
• A letter names a number array and a string array, apart from the plain variable: A, A(3), A$ and A$(3) are four different things.
• The number arrays share room for 1,024 elements, with 16 bytes each; the string arrays share 512 elements, whose text is in the strings' pool. Elements start at 0 and empty. Too many gives SORRY?; MEM shows what is left.
• An index outside the array, an array that was never dimensioned, or DIM of a name twice gives HOW?. The wrong number of indices gives WHAT?. RUN and NEW remove all the arrays, so a program dimensions them in its first lines.

Strings

Text is kept in string variables, A$ to Z$ (the name, then a $). They are separate from the numbers: A and A$ are two variables. Type the $ on its key in NUM (the one STO has above it, row 2 right of =), or from the third page of the keyword map. All the strings share one pool of 4,096 characters; one string can be up to 255 characters long, and a variable that was never set is empty. RUN and NEW empty them all.

10 A$="HELLO"
20 B$=A$+", WORLD"
30 PRINT B$;" HAS ";LEN(B$);" LETTERS"
40 IF LEFT$(B$,1)="H" THEN PRINT "STARTS WITH H"
50 INPUT "YOUR NAME";N$
60 PRINT "HI ";N$

• A$="text", A$=B$+C$: + joins strings. LET is optional. Text is kept as typed, lowercase too. PRINT takes strings and numbers in any order.
• INPUT A$ takes the whole line typed. With no prompt it shows A$? .
• IF A$="X", and <> < > <= >=: strings compare by their character codes, then by length. Both sides must be strings. The answer is 1 or 0, as with numbers.
• An answer longer than 255 characters, or strings that together would not fit the pool, give SORRY?; the variable keeps its old value.

A string can be given wherever a name is wanted: LOAD A$, SAVE "X"+A$, PLAYMIDI A$, PLAYWAV "TONES/TONE"+STR$(N).

7. Statements

8. The screen, sound and keys

Text

The text fills 9 lines of 31 characters under the status bar, and scrolls up when it reaches the bottom.

• CLS clears the screen and puts the text cursor at the top left.
• AT col,row moves it, from 0,0 to 30,8, for the next PRINT.

Graphics

The screen is 250 × 122 pixels, with x from 0 (left) to 249 and y from 0 (top) to 121. A colour of 1 is black (the default), 0 white, which erases.

The shapes are the calculator's own, in its firmware, and Plus42 draws with the same ones: PEN, BOX, ELLIPSE and POLYGON there, with DLINE for LINE. Plus42 counts from 1,1, so a position there is one more than here, and its pen starts at 1, an outline. Here, until a PEN, a shape that leaves out t is filled.

Drawing and text share the screen. While a program runs the status bar isn't redrawn, so the program can use the whole screen; it comes back at the prompt.

Sound and time

• TONE n plays the calculator's tone n, 0 (low) to 9 (high), or 10 for the error sound. The program waits until it has played.
• PLAYMIDI "name" plays the song /MIDI/name.mid from the calculator's drive (the same songs as the MIDI Player app) and goes on at once: the music plays in the background while the program draws, reads keys or waits. The song keeps playing after the program ends, until it finishes, STOPMIDI stops it, or you leave BASIC. The name is as it is on the drive, in quotes (or without quotes if it has no spaces); up to 28 characters. A song that isn't there, or isn't a MIDI file the synthesizer can play, gives HOW?; one over 128 KB gives SORRY.
• STOPMIDI stops the song.
• PLAYWAV "name" plays the WAV file /SOUNDS/name.wav on the calculator's drive and goes on at once. A / in the name is a folder: PLAYWAV "TONES/TONE3". A file that isn't there or can't be played gives HOW?. The speaker plays one sound at a time, so a new PLAYWAV, PLAYMIDI or TONE replaces the one playing.
• STOPWAV stops the sound; it does the same as STOPMIDI.
• MIDI() is 1 while a song (or a WAV) is playing and 0 when it isn't, so a program can wait for the end: WAIT 100 in a loop while MIDI() is 1.
• WAIT ms pauses that many milliseconds; R/S still stops the program during it.

Keys: KEY()

While a program runs, the keys pressed (except R/S and ON, which stop it) are kept for KEY(). Each call gives the next one, in the order pressed, as its row and column from 1, or 0 when there's none left:

10 REM MOVE A BOX WITH 4 AND 6, R/S STOPS
20 CLS:X=120
30 BOX X,55,8,8
40 K=KEY()
50 IF K=0 THEN WAIT 20:GOTO 40
60 BOX X,55,8,8,0
70 IF K=52 THEN X=X-8
80 IF K=54 THEN X=X+8
90 GOTO 30

Line 50 waits for a key, asleep, 20 ms at a time. Line 60 erases the box (colour 0) before it moves. A single pixel (PSET) is hard to see on the calculator's screen: for something that moves, draw a BOX.

9. Saving programs

Programs are saved on the calculator's drive as plain text files, NAME.BAS, in the folder /BIN/APPS/BASIC/. A name has up to 20 letters, digits, _ or -. The quotes can be left out: LOAD RINGS3D is LOAD "RINGS3D". Inside quotes a name can also have spaces: SAVE "My Ring"; without quotes a name ends at the first space. The SAVE, LOAD and ERASE keys of the keyword map type the word and a space, no quote. Lower case is the same name in capitals: "Ring_3d" is saved and listed as RING_3D.

On a computer. In USB Drive mode the files are in BIN/APPS/BASIC. A .BAS file is the program as LIST shows it, so you can read and write programs in any text editor. Lines without a number are skipped when loading.

AUTOSAVE. When you leave BASIC, the program in memory is saved as AUTOSAVE.BAS, and loaded again when BASIC starts. It's the program as it is at that moment, whatever you saved or loaded under other names meanwhile: after LOAD "GAME" and leaving, BASIC starts with GAME. It's written when you leave by ON (and ENTER to confirm), when you hold ON to turn off, and when the Sleep Timer or an empty battery turns the calculator off. It isn't written if the calculator crashes or is reset, so SAVE a program you can't lose. FILES doesn't list it.

10. Errors

The three messages of the original Tiny BASIC, plus BREAK. In a program each also says the line: HOW? IN 120.

11. Examples

These come with the project, in sim/drive/BIN/APPS/BASIC/. Copy them to BIN/APPS/BASIC on the calculator's drive, then LOAD "PRIMES" and RUN.

HELLO

10 REM THE FIRST PROGRAM
20 CLS
30 PRINT "HELLO FROM THE PX-42F!"
40 FOR I=1 TO 5
50 PRINT I;" SQUARED IS ";I*I
60 NEXT I
70 TONE 5

PRIMES

10 REM PRIMES BELOW 100
20 FOR N=2 TO 100
30 FOR D=2 TO SQR(N)
40 IF N MOD D=0 THEN 70
50 NEXT D
60 PRINT N;" ";
70 NEXT N
80 PRINT

GUESS

10 REM GUESS THE NUMBER, 1 TO 100
20 N=RND(100):T=0
30 INPUT "GUESS? ",G
40 T=T+1
50 IF G<N THEN PRINT "HIGHER":GOTO 30
60 IF G>N THEN PRINT "LOWER":GOTO 30
70 PRINT "YES, IN ";T;" GUESSES"
80 TONE 9

SPIRAL

10 REM A SPIRAL OF LINES: R/S STOPS
20 CLS:DEG
30 X=125:Y=61
40 FOR A=0 TO 1440 STEP 15
50 R=A/24
60 U=125+R*COS(A):V=61+R*SIN(A)
70 LINE X,Y,U,V
80 X=U:Y=V
90 NEXT A
100 WAIT 3000

JUKEBOX

Plays /MIDI/Canon.mid (put a song of that name there, or change the name in line 50) and stops when you press a key.

10 REM PLAYS A SONG FROM /MIDI
20 CLS
30 PRINT "PLAYING CANON"
40 PRINT "ANY KEY STOPS IT"
50 PLAYMIDI "Canon"
60 WAIT 100
70 IF KEY()<>0 THEN STOPMIDI
80 IF MIDI() THEN GOTO 60
90 PRINT "DONE"

SINE

10 REM SIN AND COS, PLOTTED
20 CLS:RAD
30 LINE 0,61,249,61:LINE 125,0,125,121
40 FOR X=0 TO 249
50 T=(X-125)/20
60 PSET X,61-40*SIN(T)
70 PSET X,61-40*COS(T)
80 NEXT X
90 WAIT 3000

SHAPES

Each kind of shape, a page at a time, with PEN; a key goes on. Line 650 draws over the ball with a white pen.

10 REM SHAPES: WHAT THE CALCULATOR DRAWS. A KEY GOES ON
20 REM PEN T,C SETS THE THICKNESS AND COLOUR OF WHAT FOLLOWS
30 DEG:DIM X(5),Y(5)
100 REM ----- THE WHOLE SCREEN -----
110 CLS:PEN 1
120 BOX 0,0,250,122:LINE 0,0,249,121:LINE 0,121,249,0
130 GOSUB 900
200 REM ----- A STAR OF LINES, THEN EACH THICKNESS -----
210 CLS:PEN 1
220 FOR A=0 TO 345 STEP 15
230 LINE 69,61,INT(69.5+56*COS(A)),INT(61.5+56*SIN(A))
240 NEXT A
250 LINE 139,19,239,19
260 PEN 2:LINE 139,39,239,39
270 PEN 4:LINE 139,61,239,61
280 PEN 8:LINE 139,83,239,83
290 PEN 16:LINE 149,105,229,105
295 GOSUB 900
300 REM ----- BOXES: OUTLINES, FILLED, WHITE INSIDE -----
310 CLS
320 PEN 1:BOX 9,9,70,45
330 PEN 2:BOX 89,9,70,45
340 PEN 4:BOX 169,9,70,45
350 PEN 0:BOX 9,64,110,50:BOX 129,64,110,50
360 PEN 0,0:BOX 34,77,60,24
370 PEN 3,0:BOX 141,72,86,34
380 GOSUB 900
400 REM ----- CIRCLES AND ELLIPSES -----
410 CLS
420 PEN 1:CIRCLE 41,31,28
430 PEN 3:CIRCLE 124,31,28
440 PEN 7:CIRCLE 207,31,28
450 PEN 0:ELLIPSE 67,91,60,26
460 PEN 0,0:ELLIPSE 67,91,30,12
470 PEN 2:ELLIPSE 189,91,50,20
480 GOSUB 900
500 REM ----- POLYGONS: A FILLED STAR, WITH ITS HOLE; A HEXAGON -----
510 CLS
520 PEN 0:N=5:S=144:C=66:GOSUB 800
530 PEN 2:N=6:S=60:C=186:GOSUB 800
540 GOSUB 900
600 REM ----- A WHITE PEN ERASES: A BALL HOPS ACROSS -----
610 CLS
620 FOR D=19 TO 229 STEP 30
630 PEN 0:CIRCLE D,61,14
640 WAIT 300
650 PEN 0,0:CIRCLE D,61,14
660 NEXT D
670 END
800 REM N CORNERS, S DEGREES APART, AROUND C,62
810 A=-90
820 FOR I=0 TO N-1
830 X(I)=INT(C-0.5+50*COS(A)):Y(I)=INT(61.5+50*SIN(A))
840 A=A+S
850 NEXT I
860 POLYGON N,X,Y
870 RETURN
900 REM WAIT FOR A KEY
910 IF INKEY$="" THEN WAIT 20:GOTO 910
920 RETURN

CATCHER

A game that shows the graphics and the sound. Stars and rocks fall; 4 and 6 (or ▲ ▼) move the basket. A star caught plays a tone without stopping the game (PLAYWAV "TONES/TONE"+STR$(C)), one higher for each star in a row; a rock costs a life, with sparks drawn by LINE and the error sound (TONE 10). Every 10 stars the game speeds up, with a jingle. Three rocks and it's over; ENTER plays again, R/S stops.

10 REM STAR CATCHER: CATCH THE STARS, DODGE THE ROCKS
20 REM 4 AND 6 (OR THE ARROWS) MOVE THE BASKET, R/S QUITS
30 REM GRAPHICS: LINE BOX PSET AT. SOUND: TONE AND PLAYWAV
40 DIM X(3),Y(3),T(3)
50 H=0
100 REM ----- TITLE: A BURST OF LINES, A FANFARE -----
110 CLS:RAD
120 FOR A=0 TO 6.2 STEP 0.2
130 LINE 121,66,121+55*COS(A),66+38*SIN(A)
140 NEXT A
150 BOX 66,58,110,17,0
160 LINE 66,58,175,58:LINE 66,74,175,74
170 AT 9,4:PRINT "STAR CATCHER";
180 AT 4,8:PRINT "ENTER: PLAY  R/S: QUIT";
190 TONE 3:TONE 5:TONE 7:TONE 9
200 REM TWINKLE IN THE CORNERS UNTIL ENTER
210 N=RND(60)-1:IF RND(2)=1 THEN N=N+190
220 PSET N,RND(80)+13,RND(2)-1
230 K$=INKEY$:IF K$<>CHR$(13) THEN WAIT 20:GOTO 210
300 REM ----- A NEW GAME -----
310 CLS:S=0:L=3:V=2:C=0:P=113:G=10
320 FOR I=0 TO 3:T(I)=0:NEXT I
330 FOR I=1 TO 40:PSET RND(250)-1,RND(80)+26:NEXT I
340 LINE 0,121,249,121
350 GOSUB 900:GOSUB 800
400 REM ----- EACH FRAME: THE KEYS, THEN EVERYTHING FALLS -----
410 K$=INKEY$:D=0
420 IF K$="4" OR K$=CHR$(30) THEN D=-12
430 IF K$="6" OR K$=CHR$(31) THEN D=12
440 IF D THEN BOX P,112,24,8,0:P=P+D:IF P<0 THEN P=0
450 IF P>226 THEN P=226
460 IF D THEN GOSUB 800
500 FOR I=0 TO 3
510 IF T(I)=0 THEN GOSUB 600:GOTO 590
520 BOX X(I)-3,Y(I)-3,7,7,0
530 Y(I)=Y(I)+V
540 IF Y(I)>=110 THEN GOSUB 700:GOTO 590
550 IF T(I)=1 THEN LINE X(I)-3,Y(I),X(I)+3,Y(I):LINE X(I),Y(I)-3,X(I),Y(I)+3
560 IF T(I)=2 THEN BOX X(I)-3,Y(I)-3,7,7,1:PSET X(I)-1,Y(I)-1,0
590 NEXT I
595 IF L=0 THEN 1000
598 WAIT 20
599 GOTO 410
600 REM ----- MAYBE A NEW STAR OR ROCK IN SLOT I -----
610 IF RND(12)>1 THEN RETURN
620 X(I)=RND(234)+7:Y(I)=29:T(I)=1
630 IF RND(10)<=2+INT(S/15) THEN T(I)=2
640 RETURN
700 REM ----- SLOT I REACHED THE BASKET'S LINE -----
710 Z=T(I):T(I)=0
720 IF X(I)<P-2 OR X(I)>P+25 THEN 770
730 IF Z=2 THEN 780
740 S=S+1:C=C+1:IF C>9 THEN C=9
750 PLAYWAV "TONES/TONE"+STR$(C)
760 IF S=G THEN GOSUB 850
765 GOSUB 900:GOSUB 800:RETURN
770 IF Z=1 THEN C=0
775 GOSUB 800:RETURN
780 L=L-1:C=0:GOSUB 950:GOSUB 900:GOSUB 800:RETURN
800 REM ----- THE BASKET -----
810 BOX P,112,24,8,0
820 LINE P,112,P+3,119:LINE P+23,112,P+20,119:LINE P+3,119,P+20,119
830 LINE P+1,115,P+22,115
840 RETURN
850 REM ----- NEXT LEVEL: FASTER, AND A JINGLE -----
860 V=V+1:G=G+10
870 AT 11,4:PRINT "LEVEL ";V-1;
880 TONE 5:TONE 7:TONE 9
890 BOX 0,61,250,12,0:RETURN
900 REM ----- SCORE, BEST, LIVES -----
910 AT 0,0:PRINT "SCORE ";S;"  ";
920 AT 13,0:PRINT "BEST ";H;"  ";
930 FOR J=0 TO 2:BOX 218+J*10,15,8,8,1:IF J>=L THEN BOX 219+J*10,16,6,6,0
940 NEXT J
945 LINE 0,25,249,25:RETURN
950 REM ----- A ROCK HIT: SPARKS AND THE ERROR SOUND -----
960 FOR A=0 TO 3.2 STEP 0.4
970 LINE X(I),111,X(I)+12*COS(A),111-12*SIN(A)
980 NEXT A
985 TONE 10
990 BOX X(I)-13,98,27,14,0:RETURN
1000 REM ----- GAME OVER: A FALLING SCALE -----
1010 IF S>H THEN H=S
1020 BOX 50,47,150,52,0
1030 LINE 50,47,199,47:LINE 199,47,199,98:LINE 199,98,50,98:LINE 50,98,50,47
1040 AT 11,3:PRINT "GAME OVER";
1050 AT 11,5:PRINT "SCORE ";S;
1060 FOR N=9 TO 0 STEP -3:TONE N:NEXT N
1070 IF INKEY$<>"" THEN 1070
1080 AT 10,6:PRINT "ENTER: AGAIN";
1090 K$=INKEY$:IF K$<>CHR$(13) THEN WAIT 20:GOTO 1090
1100 GOTO 300

12. Limits

13. Quick reference