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 This page contains articles on the TI99/4a. There is a brief linked index to help you find something useful.

Web article two- published March 1999
Includes:
Tips on programming menu choices; Using the various TI99/4A graphics programming packages with examples; how to use Basic PRINT USING; Jim Peterson's Tips No 65

MENU CHOICES

TIPS was a commercial clip art program for the TI99/4A.
The TIPS program allows you to input the name of a graphic - but it goes a little farther than that. You do not have to key in the full name of the graphic, just enough to identify it. If there is more than one possible match, the program selects the first possible.
For example, if the graphics on file are ANT, APE, APPLE, when you select A you will have an ANT, if you type AP you will have an APE and for APP you get an APPLE.
We can copy this into our Basic programs when a typed selection is required, like this:
1 ! AS TIPS CHOICE
2 !
3 ! INPUT AS LITTLE AS IS
4 ! REQUIRED TO IDENTIFY
5 ! CHOICE
6 !
7 ! FIRST MATCH IS
8 ! SELECTED IF MORE THAN
9 ! ONE CHOICE
10 !
92 !
93 ! DATA IS SORTED
94 !
100 DIM A$(25)
110 DATA BACK,BAG,BOA,BODY,B
OND,BONE,CAB,CABIN,CABINET,C
AKE,CAR,CARD,CARE,CAROL,CARP
,CART,CASE,CASK,CAT,,,
120 FOR T=1 TO 19 :: READ A$
(T):: NEXT T
130 REM
140 PRINT "SELECT FROM":
150 FOR T=1 TO 19 :: PRINT A$(T);" ";:: NEXT T
160 PRINT "":"":"":""
170 REM
180 INPUT B$
190 LA=LEN(B$)
200 FOR T=1 TO 19
210 IF B$=SEG$(A$(T),1,LA)THEN 240
220 NEXT T
230 PRINT "UNABLE TO MATCH":"":"" :: GOTO 140
240 PRINT "MATCHED ON ";A$(T):"":"":"":""
250 GOTO 130
260 END
Users of other computers will be used to more sophisticated selection routines, and we can go a little way towards these in Basic - not quite as fast as machine code perhaps, but usable... in the following listing, the four arrow keys are usable... see if you can follow the different inputs for different choices. And don't type too fast when inputting a choice...
100 ! AS PC CHOICE
110 !
120 ! INPUT AS LITTLE AS IS
130 ! REQUIRED TO IDENTIFY
140 ! CHOICE
150 !
160 ! FIRST MATCH IS
170 ! DISPLAYED. TYPE MORE
180 ! IF REQUIRED OR USE
190 ! ARROW KEYS E&S (WITH
200 ! FCTN KEY! )
210 !
220 !
230 ! DATA IS SORTED
240 !
250 DIM A$(25)
260 !
270 DATA BACK,BAG,BOA,BODY,B
OND,BONE,CAB,CABIN,CABINET,C
AKE,CAR,CARD,CARE,CAROL,CARP
,CART,CASE,CASK,CAT,FORD,FOR
K,FORT,,,
280 FOR T=1 TO 22 :: READ A$(T):: NEXT T
290 REM
300 PRINT "SELECT FROM":
310 FOR T=1 TO 22 :: PRINT A$(T);" ";:: NEXT T
320 PRINT "":"":"":""
330 PRINT "after first letter typed, use fctn e and fctn x to
move up and down list or carry on typing":"":"":
340 ROW=24 :: COL=3
350 CALL HCHAR(ROW,COL,30)::
CALL KEY(5,X,Y):: IF Y>0 TH
EN 370 ELSE CALL HCHAR(ROW,
COL,32):: GOTO 350
360 !
370 CALL HCHAR(ROW,COL,X):: COL=COL+1 :: B$=B$&CHR$(X):: LB=LEN(B$)
380 !
390 FOR T=1 TO 22
400 IF B$=SEG$(A$(T),1,LB)THEN DISPLAY AT(24,1):A$(T):: GOTO 460
410 !
420 IF B$<A$(T)THEN T=T-
1 :: CALL SOUND(100,140,4)::
DISPLAY AT(24,1):A$(T):: B$
=SEG$(B$,1,1):: LB=LEN(B$)::
GOTO 460
430 !
440 NEXT T :: CALL SOUND(100,200,4):: T=22 :: DISPLAY AT(24,1):A$(T)
450 !
460 ! FIRST LETTER CHOSEN
470 ! NOW IS IT WHAT WE WANT?
480 CALL HCHAR(23,3,32,28)
490 CALL HCHAR(23,3,95,28)
500 !
510 CALL KEY(5,X,Y):: IF Y<1 THEN 510
520 IF X=13 THEN 640 ! GOT IT
530 IF X=11 AND T>1 THEN T=T-1 :: DISPLAY AT(24,1):A$(T):: B$=SE
G$(A$(T),1,LB):: GOTO 460
540 IF X=11 AND T<2 THEN CALL SOUND(200,200,4):: GOTO 460
550 IF X=10 AND T<22 THE
N T=T+1 :: DISPLAY AT(24,1):
A$(T):: B$=SEG$(A$(T),1,LB):
: GOTO 460
560 IF X=10 AND T=22 THEN CA
LL SOUND(200,200,4):: GOTO 460
570 IF X=8 AND LB>1 THEN B$=
SEG$(B$,1,LB-1):: LB=LEN(B$)
:: GOTO 390
580 IF X=9 AND LB<LEN(A$(T)
)THEN B$=SEG$(A$(T),1,LB+1):
: :: LB=LEN(B$):: GOTO 390
590 !
600 IF X<32 THEN 390
610 !
620 CALL SOUND(100,800,13)
630 B$=B$&CHR$(X):: DISPLAY AT(24,1):B$ :: LB=LEN(B$):: GOTO 390
640 CALL CLEAR :: PRINT "CHOICE WAS":"":A$(T)
650 RUN

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====================================

HIGH RESOLUTION GRAPHICS


The links to jbm103 and TML are to disk images for TI emulators.
In the Reader to Reader column of MICROpendium, March 1992, Chuck McConnell of Ohio wrote asking for a way to plot graphics at pixel level without using a disk drive (which rules out such fun programs as The Missing Link and JBM103).
My first TI computer was a TI99/4, which did not HAVE a high resolution mode of any sort, and given a long standing interest in graphics, I have since that time tried (almost) every graphics program available.

TI Logo was designed for the TI99/4, and in the absence of pixel graphics, utilised a routine which continually redefined characters (or tiles) as you drew on the screen. Sooner or later you ran out of characters, and in the colourful terms of TI Logo, you ran out of ink!

Back in 1982, we were blessed with a routine in TI Basic which allowed high resolution graphics plotting, continually redefining characters, thanks to Peter Brooks, a felow founder member of the first UK user group. This was painfully slow, and as TI Basic does not have CALL CHARPAT had to make use of a large string array, and also boolean algebra had to be done the hard way.

Then along came Extended Basic, which I think most people now have? And Gary Harding rewrote Peter's routine making use of CHARPAT and OR. The program below is an example of its use. The maths is placed in a subroutine, so the only variable you need to avoid in your inserted routines is S, which keeps track of which character we are redefining.
100 ! hi res plotting - ti ex bas only
110 ! after brooks, harding etc.
120 ! initialise:
130 S=31 :: FOR C=0 TO 14 :: CALL COLOR(C,16,2) :: NEXT C
140 CALL HCHAR(1,1,S,768) :: CALL SCREEN(2)
150 !
160 !
170 !
180 ! YOUR PROGRAM HERE
190 !
200 !
210 FOR COL=40 TO 140 STEP 100 :: FOR ROW=20 TO 160
220 CALL PLOT(ROW,COL,S) :: NEXT ROW :: NEXT COL
230 !
240 FOR RAD=0 TO 6.5 STEP 0.0125
250 CALL PLOT(36*SIN(RAD)+99,36*COS(RAD)+76,S) :: NEXT RAD
260 !
270 !
280 !
10000 GOTO 10000
10010 STOP
10020 !
30000 SUB PLOT(R,C,S)
30010 IF R>190 OR C>254 THEN SUBEXIT
30020 IF R<1 OR C<1 THEN SUBEXIT
30030 R=INT(R+.4) :: C=INT(C+.4)
30040 Y=INT(R/8+0.875) :: X=INT(C/8+0.875)
30050 H$="0123456789ABCDEF"
30060 B=C-X*X+8 :: P=2*R-16*Y+16+(B<5)
30070 IF B>4 THEN B=B-4
30080 CALL GCHAR(Y,X,H)
30090 IF H>31 THEN 30120 ELSE IF S=143 THEN SUBEXIT
30100 S=S+1 :: D$=RPT$("0000",4) :: CALL CHAR(S,D$)
30110 CALL HCHAR(Y,X,S) :: H=S :: GOTO 30130
30120 CALL CHARPAT(H,D$)
30130 N=(POS(H$,SEG$(D$,P,1),1)-1)OR(S^(4-B))
30140 D$=SEG$(D$,1,P-1)&SEG$(H$,N+1,1)&SEG$(D$,P+1,16-P)
30150 CALL CHAR(H,D$) :: SUBEND
31000 ! ORIGINAL ROUTINE TIDINGS OCT 1982

Yes it is just a little slow, but remember it is all Extended Basic with no extras required, no disk drive, no 32k ram!
Chuck also wrote directly to me, asking about using the Drawnplot routines to be found in the Triton module Super Extended Basic.
When driven from a program, Drawnplot has only a limited set of commands, but sufficient for our purposes. The biggest drawback -to me! - is that the image does not appear on the screen until it is finished. For a lengthy chaotic or fractal image this can mean a long time with nothing obvious happening, so in the program below I have added a screen counter. During processing some odd characters appear on the screen - ignore them! - Drawnplot does not really like you to use the screen while it is plotting!

The program below is a routine for a chaotic graphics plot, and really does take a very long time to finish! The end result is interesting as total order, represented by a single line, becomes total chaos after repeated bifurcation.Super Extended Basic requires that you have the 32k ram attached, and you enter the graphics mode by typing the command sequence:

 CALL FILES(2)
 NEW
 CALL INIT
 CALL DRAWNPLOT

Now you can input or load your program as follows:
10 ! high resolution graphics using
20 ! triton super extended basic and 32k ram
30 ! after brooks, harding etc
40 !
100 CALL LINK("GCLEAR")
110 ! ORBITDGM PROGRAM
120 ! OR insert your program here:
130 FOR C=-2 TO 0.25 STEP .00625
140 X=0 :: M=160*(C+2) :: FOR I=0 TO 200
150 X=X*X+C :: IF I<50 THEN 170
160 N=(180/4)*(2-X) :: CALL PSET(M,N)
170 NEXT I
172 NEXT C
180 CALL LINK("MOVE",80,160)
190 CALL LINK("LABEL","Press E to Exit")
200 CALL LINK("SHOW")
210 STOP
10000 SUB PSET(X,Y)
10010 CALL LINK("MOVE",X,Y) :: CALL LINK("DRAW",X,Y)
10020 SUBEND
- - - - -
Above code corrected 2020 after jonathan contacted me with a problem- thanks! 21 years for an error to be reported...

It would be amiss of me not to make this a complete article by covering some other possibilities...
For Myarc Extended Basic, you require the Myarc module, Myarc expansion memory, and the disk and rom chip supplied with the module. The listing immediately above needs the following changes:

100 CALL GRAPHICS(3)

180 REM
190 CALL WRITE(0,160,80,"* done *")
200 REM

10010 CALL POINT(1,X,Y)

MYARC XB is fast and has the unique ability of being able to tell you if a pixel is on or off - and like the Missing Link you can have sprites in high resolution mode!
- - - - -
For THE MISSING LINK, a commercial disk from Texaments requiring any Extended Basic plus 32k ram and disk system, the following amendments are required to the program:
100 CALL LINK("CLEAR")

180 REM
190 CALL LINK("PRINT",160,80,"* DONE *")
200 REM

10010 CALL LINK("PIXEL",X,Y)

- - - - -
There is a French utilitiy in circulation called JBM103, which would require the following:
100 CALL LOAD(-31890,56,0) :: CALL LOAD(-31964,56,0)
105 CALL LINK("CLEAR") :: CALL LINK("SCR2")

180 REM
190 REM
200 REM

10010 CALL LINK("POINT",16,X,Y)

- - - - - - - -
The graphics enthusiast thus has a choice of programming environments- each choice has something to offer. My present first choice tends to be The Missing Link, but there are occaisions when Myarc XB is necessary.
Both The Missing Link and JBM103 can save your art forms in TI Artist format, and I have lost count of the number of utilities you can use with this format! Enjoy.
Stephen Shaw UK April 1992
You can see some of these graphics listings in a more modern language that you can run on a Mac, Windows or Unix (Linux) machine on my sdlBasic language page.
And here are a few more graphics listings - small listings, complex graphics. There are written for The Missing Link, but the data above will help you use other TI graphics programs:
100 REM CIRCLES
110 REM JE CONNETT/PWH MOON/
S SHAW 1990
120 SIDE=20
130 REM
140 CALL LINK("CLEAR")
150 FOR I=1 TO 150 :: FOR J=
1 TO 150
160 X=I*SIDE/150 :: Y=J*SIDE
/150 :: C=INT(X*X+Y*Y):: D=C
/2 :: IF D-INT(D)>.1 THEN 180
170 CALL LINK("PIXEL",I+20,J+20)
180 NEXT J :: NEXT I
190 PIC=PIC+1 :: A$="DSK2."&STR$(PIC)
200 CALL LINK("SAVEP",A$)
210 SIDE=SIDE*1.2 :: GOTO 140
220 END
===========================
100 CALL LINK("CLEAR")
110 H=240 :: V=180
120 REM
130 REM
140 X=6.10
150 Y=6.00
160 REM
170 REM
180 FOR L=1 TO 3299
190 NX=1-Y+ABS(X):: NY=X :: X=NX :: Y=NY
200 A=100+X*7-Y*7
210 B=70+X*7+Y*7
220 CALL LINK("PIXEL",A,B)
230 NEXT L
240 CALL LINK("PRINT",180,180,"END")
250 X=8.30 :: Y=8.02
260 FLAG=FLAG+1 :: IF FLAG>2
THEN 260 ELSE IF FLAG>1 THE
N X=8.56 :: Y=3.76 :: GOTO 1
60 ELSE GOTO 160 
--------------------------------- 
100 CALL LINK("CLEAR")
110 H=240 :: V=180
120 REM
130 REM
140 X=-.100000000001
150 Y=0
160 REM
170 REM
180 FOR L=1 TO 5299
190 NX=1-Y+ABS(X):: NY=X :: 
X=NX :: Y=NY
200 A=100+X*14-Y*14
210 B=60+X*14+Y*14
220 CALL LINK("PIXEL",A,B)
230 NEXT L
240 CALL LINK("PRINT",180,18
0,"END")
260 GOTO 260
==============================


The article formerly here on using PRINT USING has now been moved to Rambles from TI*MES 37 which also has a further article by Mark on file protocols.

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============================

Tips from the Tigercub Issue 65.
Note: Jim died a few years back. He contributed some 72 monthly articles to TI user groups. He always formatted them for 28 column printing- here presented as he produced it. Depending on your screen size you may see one two or three columns! Each pseudo-page is separated by two short rows of equals signs:
===========
===========
If your screen is wide enough for three columns each pseudo-page will about fit onto one screen. With one or two columns you will need to scroll, sorry.

---------------------------------------




No. 65

Tigercub Software
1N6 Nnuyngwood Ave.
ZxCdmbus, OH 43XY3

*********

My three Nuts & Bolts
disks, each containing 100
or more subprograms, have
been reduced to $5.00. I am
out of printed documentation
so it will be supplied on
on disk.
My TI-PD library now has
well over 500 disks of fair-
ware (by author's permission
only) and public domain, all
arranged by"category and as
full as possible, provided
with loaders by full program
name rather than filename,
Basic programs converted to
XBasic, etc. The price is
just $1.50 per disk(!), post
paid if at least eight are
ordered. TI-PD catalog #5
and the latest supplement is
available for $1 which is
deductible from the first
order.

It is a bit of a nuisance
to have to hit Enter after
inputting a single character
such as Y or N for "yes" or
"no". CALL KEY accepts a
single character without
Enter, but has no blinking
cursor to tell you that it
is waiting. I should have
had this one in my Nuts &
Bolts years ago - the CALL
KEY WITH CURSOR subprogram!
R is the row, C is the TAB
position, V$ is the valida-
tion string, such as "YyNn",
and the character selected
is returned in K$.

30000 SUB CALLKEY(R,C,V$,K$)
30001 CALL HCHAR(R,C+2,30)::
FOR T=1 TO 3 :: CALL KEY(0,
K,S):: IF S<>0 THEN 30004
30002 NEXT T :: CALL HCHAR(R
,C+2,20):: FOR T=1 TO 3 :: C
ALL KEY(0,K,S):: IF S<>0 THE
N 30004
30003 NEXT T :: GOTO 30001
30004 IF POS(V$,CHR$(K),1)=0
THEN 30001 ELSE K$=CHR$(K)
30005 SUBEND

And for a demonstration of
the use of that subprogram,
here is a little game that
no one will ever play to the
end -

100 DISPLAY AT(3,6)ERASE ALL
:"THE ULTIMATE TEST":"":" An
swer the question with a num
ber according to whether the
number or color shown,"
110 DISPLAY AT(8,1):"or the
note sounded, was 1stor 2nd
or 3rd, etc."
120 DISPLAY AT(23,6):"PRESS
ANY KEY" :: DISPLAY AT(23,6)
:"press any key" :: CALL KEY
(0,K,SS):: IF SS=0 THEN 120
ELSE CALL CLEAR
130 DATA 2,BLACK,3,GREEN,5,B
LUE,9,RED,12,YELLOW,14,PURPL
E
140 FOR J=1 TO 6 :: READ C(J
),C$(J):: CT$=CT$&CHR$(J)::
W$=W$&CHR$(J+48):: NEXT J ::
T=2 :: DL=500 :: V$="12"
150 RANDOMIZE :: T$,NN$=CT$
:: FOR J=1 TO T :: X=INT(RND
*LEN(T$)+1):: X$=SEG$(T$,X,1
):: T$=SEG$(T$,1,X-1)&SEG$(T
$,X+1,255):: Y(J)=ASC(X$)
160 X=INT(RND*LEN(NN$)+1)::
X$=SEG$(NN$,X,1):: NN$=SEG$(
NN$,1,X-1)&SEG$(NN$,X+1,255)
:: S(J)=ASC(X$):: NEXT J ::
FOR J=1 TO T

===========
===========
170 Z(J)=INT(89*RND+10):: FO
R K=1 TO J-1 :: IF Z(J)=Z(K)
THEN 170
180 NEXT K :: NEXT J :: CALL
CLEAR :: CALL COLOR(3,16,1,
4,16,1)
190 FOR J=1 TO T :: CALL SCR
EEN(C(Y(J))):: CALL SOUND(-9
99,110*S(J),0):: DISPLAY AT(
12,12):Z(J):: FOR D=1 TO DL
:: NEXT D :: NEXT J
200 CALL CLEAR :: CALL SCREE
N(16):: CALL COLOR(3,2,1,4,2
,1):: X=INT(3*RND+1):: W=INT
(T*RND+1):: ON X GOTO 210,23
0,210
210 IF X=1 THEN Q$=C$(Y(W))E
LSE IF X=3 THEN Q$=STR$(Z(W)
)
220 DISPLAY AT(12,1):"WHICH
WAS ";Q$ :: GOTO 240
230 CALL SOUND(1,30000,30)::
DISPLAY AT(12,1):"WHICH WAS
?" :: FOR D=1 TO 200 :: NEXT
D :: CALL SOUND(500,110*S(W
),0)
240 CALL CALLKEY(12,20,V$,K$
):: Q=ASC(K$)-48
250 IF Q=W THEN DISPLAY AT(1
5,12):"RIGHT!" ELSE DISPLAY
AT(15,12):"WRONG!"
260 IF Q=W THEN DL=DL-50 ELS
E DL=DL+50
270 IF DL<100 THEN DL=500 ::
T=T+1 :: V$=SEG$(W$,1,T)
280 GOUO 150
290 SUB CALLKEY(R,C,V$,K$)
300 CALL HCHAR(R,C+2,30):: F
OR T=1 TO 3 :: CALL KEY(0,K,
S):: IF S<>0 THEN 330
310 NEXT T :: CALL HCHAR(R,C
+2,20):: FOR T=1 TO 3 :: CAL
L KEY(0,K,S):: IF S<>0 THEN
330
320 NEXT T :: GOTO 300
330 IF POS(V$,CHR$(K),1)=0 T
HEN 300 ELSE K$=CHR$(K)
340 SUBEND

I have warned repeatedly
over the years, in these
Tips and in Micropendium and
elsewhere, that printing
program listings through the
Funlweb Formatter usually
results in garbled listings
that cannot be keyed in cor-
rectly - but I still see the
garbled listings published.
Here is a fix to the Funlweb
FO file that will partially
solve the problem -
Boot DSKU. Select 1. File
Utilities. Select 5. Find
String. Enter filename FO
and the drive number. Enter
H for hex. Enter the string
2A23214026 . Enter replace
string 7C2321605C . When the
string is found, enter R for
replace, then CTRL W, hit
Enter twice to accept the
defaults. Thereafter, use
FCTN Z instead of & to under
line, FCTN C instead of @ to
double-strike, and FCTN A
instead of * to call a value
added file. I don't know why
Texas Instruments didn't do
that in the first place, and
I wonder why the McGoverns
didn't make that fix.
Now, can anyone tell me
how to replace the ^, which
tends to disappear, and the
period, which will make the
whole line disappear if it
happens to be at the begin-
ning of the line?

If you are one of the few
who are still interested in
recreational computing - the
use of the computer to solve
puzzles and math problems
just for the fun of it - you
might be interested in Rec-
reational and Educational
Computing, published 8 times
a year at xyz tyulet Terrace
(REC is no more alas) . The
annual subscription is $36.
Program listings are in dia-
lects of Basic other than TI
but usually not hard to con-
vert.
That is where I found this
ridiculously short, simple
and fast card shuffling rou-
tine.

===========
===========

100 DIM C(52)
110 FOR X=1 TO 52 :: C(X)=X
:: NEXT X
120 FOR X=52 TO 1 STEP -1 ::
I=INT(RND*X+1)
130 T=C(I):: C(I)=C(X):: C(X
)=T :: NEXT X

In the same place, I read
a routine to extract a root
to 16-digit accuracy instead
of the 8 digits available
on a PC from the basic for-
mula ROOT=NUMBER^(1/POWER).
We don't need it - our obso-
lete 16k 16-bit computer can
give us 14-digit accuracy
from the basic formula!

The same publication gave
me the idea for this little
game -

100 DISPLAY AT(3,6)ERASE ALL
:"THE GAME OF N":"":"You and
the computer will take tu
rns adding to a num- ber to
reach a goal."
110 DISPLAY AT(8,1):"If you
reach the goal, you win. Yo
u get to go first andyou sho
uld be able to win almost
every time."
120 RANDOMIZE :: N=INT(RND*1
5)+15 :: R=INT(4*RND+3):: S=
R+1 :: D=N-INT(N/S)*S :: T=0
130 DISPLAY AT(13,1):"The go
al is";N:"":"Maximum input i
s";R :: DISPLAY AT(19,1):RPT
$(" ",96)
140 DISPLAY AT(17,1):"Your n
umber?" :: ACCEPT AT(17,14)S
IZE(1)VALIDATE(DIGIT):A :: I
F A<1 OR A>R THEN DISPLAY AT
(15,1):"" :: GOTO 130
150 T=T+A :: DISPLAY AT(21,1
):"Total is";T :: IF T=N THE
N DISPLAY AT(23,1):"YOU WIN!
" :: GOSUB 190 :: GOTO 120
160 IF N-T<S THEN P=N-T :: T
=T+P :: DISPLAY AT(19,1):"Co
mputer adds";P :: DISPLAY AT
(21,1):"Total is";T :: DISPL
AY AT(23,1):"COMPUTER WINS!"
:: GOSUB 190 :: GOTO 120
170 IF T=0 THEN P=D ELSE IF
(N-T)/S=INT((N-T)/S)THEN P=I
NT(R*RND+1)ELSE Y=N-T :: P=Y
-INT(Y/S)*S
180 T=T+P :: DISPLAY AT(19,1
):"Computer adds";P :: DISPL
AY AT(21,1):"Total is";T ::
GOTO 140
190 DISPLAY AT(24,8):"PRESS
ANY KEY" :: DISPLAY AT(24,8)
:"press any key" :: CALL KEY
(0,K,S):: IF S=0 THEN 190 EL
SE T=0 :: RETURN

REC also printed a puzzle
which seemed so simple that
I could not see why. It goes
like this -
A game show host shows you
three curtains. Behind one
is a new car, behind the
other two are goats. You
choose one. The host, who
can peek behind the curtain,
opens one of those you did
not pick, and shows a goat.
Then he offers to let you
change your choice. Should
you switch, stand pat, or
does it make no difference?
You now have a 50-50 bet,
so it makes no difference,
right? But some very distin-
guished mathematicians were
saying you should switch, so
I wrote this computer simu-
lation to prove them wrong.
Key it in, run it, and be
surprised. Do figures lie?
Do computers lie? Is there
something wrong with my sim-
ulation?

===========
===========

100 CALL CLEAR
110 DATA CAR BEHIND,A PICKS,
HOST SHOWS,A WINS,B WINS,C W
INS
120 FOR J=1 TO 3 :: READ M$
:: DISPLAY AT(J,1):M$ :: NEX
T J :: FOR J=12 TO 14 :: REA
D M$ :: DISPLAY AT(J,1):M$ :
: NEXT J
130 FOR J=1 TO 1000 :: RANDO
MIZE :: X=INT(3*RND+1):: DIS
PLAY AT(1,13):X !RANDOMLY PL
ACE CAR
140 A=INT(3*RND+1):: DISPLAY
AT(2,13):A !PLAYER CHOOSES
150 E=INT(3*RND+1):: IF D=X
OR D=A THEN 150 :: DISPLAY A
T(3,13):D :: ! HOST PICKS CU
RTAIN WITH GOAT
160 IF A=X THEN AA=AA+1 :: D
ISPLAY AT(12,7):AA ! A DOES
NOT SWITCH
170 B=INT(3*RND+1):: IF B=A
OR B=D THEN 170
180 IF B=X THEN BB=BB+1 :: D
ISPLAY AT(13,7):BB ! B SWITC
HES
190 C=INT(3*RND+1):: IF C=D
THEN 190
200 IF C=X THEN CC=CC+1 :: D
ISPLAY AT(14,6):CC ! C CHOOS
ES RANDOMLY
210 NEXT J

Here is an improved ver-
sion of a program that was
in a Tips long ago, to strip
out the extra blanks from a
Filled and Adjusted Funlweb
Formatter file -

100 DISPLAY AT(3,6)ERASE ALL
:"TIGERCUB UNFILLER":"":" To
remove extra spaces from":"
a TI-Writer text which has":
"been Filled and Adjusted by
"
110 DISPLAY AT(8,1):"the For
matter, prior to":"reformatt
ing."
120 DISPLAY AT(15,1):"Input
file? DSK" :: ACCEPT AT(15,1
6):IF$ :: OPEN #1:"DSK"&IF$,
INPUT
130 DISPLAY AT(17,1):"Output
file? DSK" :: ACCEPT AT(17,
17):OF$ :: OPEN #2:"DSK"&OF$
140 LINPUT #1:M$ :: P=1
150 X=POS(M$,"a",P):: IF X=P
THEN P=P+1 :: GOTO 150
160 X=POS(M$," ",P):: IF X=
0 THEN PRINT #2:M$ :: GOTO 1
80
170 M$=SEG$(M$,1,X)&SEG$(M$, CE
X+2,255):: GOTO 160
180 IF EOF(1)<>1 THEN 140 ::
CLOSE #1 :: CLOSE #2

While a program is run-
ning, the computer periodi-
cally pauses for a fraction
of a second to do a "garbage
collection", getting rid of
information it no longer
needs, to make room in memo-
ry. If this pause occurs at
a critical moment in program
execution, it can cause pro-
blems. Thanks to the Sydney
User Group in Australia,
here is a CALL LOAD which
will force a garbage collec-
tion just before that criti-
cal point -
CALL LOAD(-31885,144,"",-318
58,81,169,152,0)

===========
===========

Here is a neat one from
Bruce Harrison. Key it in,
(you can skip the lines that
start with an asterisk) and
assemble it, then use ALSAVE
to imbed it in any program
that opens a disk file. Put
CALL LINK("DEVICE",DEV$) at
the beginning of the program
and change any line reading
OPEN #1:"DSK1.FILENAME" - or
  whatever - to read -
OPEN #1:DEV$&".FILENAME"
(don't forget the period be-
fore the filename!). Now you
can load the program from
any drive and it will open
the file on that same drive!

* STRING ASSIGN DEVICE NAME
* PLACES DEVICE NAME IN AN
* XBASIC STRING
* HARRISON SOFTWARE
* 8 OCTOBER 1990
* FOR USE WITH ALSAVE AND XB
* TAKES ONLY 42 BYTES MEMORY
STRASG EQU  >2010
WS     EQU  >20BA
       DEF  DEVICE
DEVICE
* USE OUR WORKSPACE
       LWPI WS
* GET THE CRU BASE IN R12
       MOV  @>83D0,R12
* GET ROM ADDRESS FOR DEVI
* IN R2
       MOV  @>83D2,R2
* ENABLE THE ROM
       LDCR @ONES,0
* ADDING 4 PUTS US AT THE
* LENGTH BYTE
       AI   R2,4
* FIRST PARAMETER
       LI   R1,1
* NOT AN ARRAY VARIABLE
       CLR  R0
* ASSIGN DEVICE NAME TO A
* STRING
       BLWP @STRASG
* CLEAR CRU, DISABLE ROM
       LDCR R0,0
* LOAD GPL WORKSPACE
       LWPI >83E0
* RETURN TO GPL INTERPRETER
       B    @>006A
* WORD TO TURN ON ROM IN CRU
ONES DATA >0101
       END


Getting short on memory,
so more next time.


Jim Peterson
===================================
Bruce Harrison is no longer with us.
Jim Peterson is no longer with us
.
The magazine referred to by Jim (we were both subscribers) is beginning to become available on line- developments are developing, so keep an eye on the website Recreational and Educational Computing

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