Atari 800 Manuel de l'opérateur télécharger pdf (Page 77)

Now start writing

a BASIC

program,

begin with:

2 DIM ES(2179i

Ther add

this

subroutine

(which

you

can delete later):

25OOO A

=90*J+

1:B

=A+89:

II B > LIMIT THEN

=LIMIT:?"LAST

LINE"

250101

5;"E$(";A;",",B,")

";CHR$(3a);

25020 FOR I-A TO B:?..8M

@,,;CHR$(PEEK)I+C));:NEXT

25030 ?CHR$(34)J

-l

+1:RETURN

Herc the

m W

symbol m€ans ihat

you

pre$

the escape key twice. Now

tyT)e

in the following direct comnands:

J= 0 ff i

p2a7

sqw

LIMIT=2179

ffi

The valu€ ofc is the address ofthe b]'ie before the lirst byte ofyoru

plograIn.

The

value of LIMIT is the length of

youl

objeci

program.

Now type

GOSUB

25000

gffiffi.

The computer will

prini

a BASIC line

onto the

screen. It will look very

strange-all sorts of strang€ characters inside a string. They are the scre€n

representation

ofyour object code. To make this lin€

part

ofyou BASIC

prgram

simply move

the cursor up to the line and

press

ffid&.

You might reassue

yourself

ihat

you

were succe$ful

by entering:

LrsT 5

S:fSW&

and vedfying that line 5 r€aly

did

go in. Now

type GOSUB 25000

again

and another line \vill be pdnted. Enter

this one the same

way

as before.

Continue this

process

of printing

ard

entering lines

until the entire object

program

has been encoded inside BASIC statem€nts. You will know

you

have

reached

this

point

when the computer

pdnts

"LAST

LINE

onto the screen.

There is

one

po$ible

hitch

with

this

process.

you

have a hex code of

$22

(decimal

value

34) anywhere in

your

code it wil be

put

onto the sceen as a

double

quotation

mark. This will confuse ihe BASIC interyreter, which

ltvill

give you

syntax

error when

you

try to enter the line. Ifihis happens, carefuly

count which

byte is th€ oft€nd€r and wdte down the index ofthe anay which

should

contain the double

quotation

mark. Then

back and replac€ th€

offending

quotation

mark with

a blank space; that will keep the BASIC

interyreter happy. Make not€

of all 6uch occumences.

When you

are done

entering th€ characters, iype in

f€w more

lines

like:

30 E$(292, 292)

CHR$(34)

This line

puts

the double

quotation

mark into

the 292nd array elem€nt by brute

force. It should come immediately

after

the lines

that declare the string. You

should have a line similar to this for each instance

ofihe double ouotation

mark.

Ma}.e sure

lhat

you

have counted

properly

and

pur

rhe double

quotarion

marks

into the right

places.

Now

your

object

program

is a

part

ofthe BASTC

plograIn.

You can

SAVE and

LOAD the BASIC program

and the object

prcgram

will be saved

and loaded

along with ii-a great

convenience. You can run the obj€ct program

running

the BASIC program

and then executing the command:

1 2 ... 72 73 74 75 76 77 78 79 80 81 82 ... 91 92

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Atari 800 Manuel de l'opérateur Page 77

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