Section 2 - Commodore Computers

156 COMPUTEI COMPUTE! May, 1Q82.lssue 1982. Issue 2-d 24
changes it. Unless 1urphy has other pl ans, this
changes it. Unless Murphy has other plans, this
completes the tests.
You .should be able to guess now what would
happen if the PRINT 'Tstatemelll statement colllained contained cursor
controls, forced quotes, commas, colons, a clear
colllrols, forced quotes, commas, colons, a clear
screen command, orr reverse lields fields (both at the
beginning and the end of the space) within the
quotes. All the info rmati on needed to answer the
quotes. All the information needed to answer the
questions is here and in the known facts off an
ordinary I INPUT T statemenl. statement. I Iff you can't guess youu
may walll want LO to try these things by repeating step II 11. .
We don't need those answers for the simple applicalio
cationn below, butt we may need lhem them forr other tasks.
The Problem Solved
Sin ce we noll' understand some of the PET's rules
in this ibis game we can try a slightly more ambitious
project: correctly picking up multifield records,
our original illlenl. intent. A routine in lines 510-1060 1060 is
used. By way of illustration, we use unformatted
data from DATA lines. Two PRINT PRJ 'T statemellls
statements
fo rmat the data on the screen, avoiding garbage
Since we now understand some of the PE'Fs rules
format the data on the screen, avoiding garbage
collection problems in thee string construction.
(The strings are acwall actuallyy constructed in high me­
mory, but that does not contribute to the garbage.)
mory, but that does not cOlllribute to the garbage.)
PRJ NT C$ does not format the data, therefore a
PRINT C$ does not format the data, therefore a
null string will result on output/input, a slight
complication if you u wantla to leave the e program
intact. The shifted-space method is used. I leave it
intacl. The shifted-space method is used. I leave il
as an exercise to the reader to try null strings else­
as an exercise to the reader to try null strings else
where on a line, while positioning ing subsequent
fields correctly. An example is given in the two
RF.M REM lines,
es. which introduce illlroduce another variable.
Admiuedly Admittedly these complications are unnecessary,
unnecessary.
they are included to make the task harder.
As each part of a line is printed, prillled, the subroutine
in 1010 I 0 places its image into an element of an array alTay
AS(line,field A$(line,field). Note that in some applications you
may not even have to go after each field. . You u may
wish to pick up one, two, three, three. or all al) four fields in
a single procedure by placing g GOSUB1010 I 0 I 0 where
you u want it. I TThere are no new concepts in the code. TheT key variables ab are: arc:
AS(I,j)
A$(I,J)
I
j
destination array
record or screen line number
field number, counted in subroutine from left
to right
cursor position before the fi eld is printed
P(J-1) PU-I ) cursor position before the field is printed
P(J) PU)
cursor position after the field is printed
Ww
screen width varying with P(J) PU>
WS
system screen width address where we adjust
CP
PS
P
screen size
syste m address of cursor position on a line
system address of cursor position on a line
forces tabbing on a null string if such must
exist. PS default is 1.
flags when we're dealing with a null string.
T he two P arrays could have been coded as si ngle
The two P arrays could have been coded as single
variables. They The)' are provided in array arra), form, for we
may need those values for something else.
may need those values for something else.
When you run this demo program, you will
see thallhe that the method works and is not all that complicated.
Here, we have purposely set up certain
roadblocks to see how far we can push the PET.
There are more uses of screen input,just as
there are more aspects to the method. Wejust
scratched thee surface. But once we have thee basics
we can go On on to bigger things.
Screen input is userul useful ror for working with strings
without th e usual penalty. I thank Jim Butterfield
without the usual penalty. I thank Jim Buttcrfield
for hinting at this in the POWER documentation
and. more impo nalllly, fOI" ofrering a va luable
and, more importantly, for offering a valuable
warning abollt about lrollble trouble spots.
10 REM SCREEN INPUT ELIZABETH I DEAL
20 P1;POS(0)
P1=POS(0)
30 PRINT"ANYTHING";:GOSUB180
40 PRINT"'":PRINT
50 PRINTA$,LEN(A$)ASC(A$+CHR$(0»
PRINTA$,LEN(A$)ASC(A$+CHR$(0))
60 END
180 P2;POS(0):P;0
P2=POS(0):P=0
19 1900 :REM IFP2;P1THENP;1
IFP2=P1THENP=1
2002 :REM IFP2;P1THENP;1:PRINTCHR$(1
IFP2=PlTHENP=l:PRINTCHR$(1
60); ;
210 POKE198,P1
220 POKE213,P2+P
230 OPEN3,3:INPUT#3,A$:CLOSE3 : 240 POKE213,39
250 POKE198,P2+P
260 RETURN
500
:
5100 W=39:WS=213:CP=198
W;39:WS;213:CP;198
520 R=3:NV=5:DIM R;3:NV;5: A$(R,NV),P(NV)
,P(NV)
530 BL$=" BL$;" ":PF$=CHR$(160):PS=1
:PS=l
540 FORI=1TOR:J=0:READ FORI;lTOR:J=0:READ A$,B,C$
550 : REM PRINT"";:IFI=2THENPRINT"*
ii " ,.
560 : REM PS=2:GOSUB1010
0 10
570 PRINT LEFT$(A$+BL$,8); ; :GOSUB1010
580 PRINT PF$+RIGHT$(BL$+STR$(B),6)
(B) +" ";:GOSUB1010
590 PRINT C$;:PS=1:GOSUB1010
:PS;1:GOSUB1010
600 PRINT:NEXTI:PRINT
610 FORI=1TOR:FORJ=1TONV
FORI;lTOR:FORJ=lTONV
620 PRINTA$(I,J);
630 NEXTJ:PRINT:NEXTI:PRINT:END
: END
640 DATA FIRST,12345,TEXT 1
650 DATA SECOND,12rTEXT D,12,TEXT 11
660 DATA THIRD,,,
THIRD",
1000 :
1010 J ;J+1:P (J);POS(0) :P;0
1010 J=J+1:P(J)=POS(0):P=0
1020 IFP(J)=P(J-1)THENP=1:PRINT IFP(J);P(J-1)THENP;1:PRINT PF$;
1030 P0KECP,P(J-l):P0KEWS,P(J)+P*PS
1030 POKECP,P(J-1) :POKEWS,P(J)+P*PS
1 040 P(J) ;P (J)+P*PS
1040 P(J)=P(J)+P*PS
10500PEN3,3:INPUT#3,A$(I,J):CLOSE3
OPEN3,3:INPUT#3,A${I,J):CLOSE3
1060 POKEWS,W:POKECP,P(J):RETURN ©
1060 POKEWS,W:POKECP,P(J):RETURN ©