Radio Shack TRS-80 model III Owner's Manual page 155

TRS-80
MODEL
III
DISK
SYSTEM
230 LSET NX$
=
MKI$ (HX1)
240 PUT
i
t
R%
245
RX
=
NX* 'USE
NEXT ALPHA* LINK
AS DEFAULT FOR NEXT RECORD
250 CLS
:
PRINT
n
TYPE <ENTER>
TO READ NEXT ALPHA* ENTRY,":
PRINT" OR
RECORD
# <EIMTER> FOR
SPECIFIC ENTRY,":
INPUT
"
OR
<
ENTER) TO QUIT'S RX
2S0
IF
0<RX
THEN 140
270 CLOSE
280 END
Notice
we've added
a
field,
nx$,
to the
record
(line 120).
nx$
will
contain
the
number
of
the
record
which comes
next
in
alphabetical sequence. This enables
us
to
proceed
alphabetically
through
the glossary,
provided
we know
which
record contains the entry
which
should
come
first.
For example, suppose the glossary contains:
record# word (WD$)
defn,
pointer to next
alpha, entry (NX$)
1
2
3
4
LEFT-JUSTIFY
BYTE
RIGHT-JUSTIFY
HEXADECIMAL
3
4
1
When we
read record 2 (byte),
it
tells
us
that
record
4 (hexadecimal)
is
next,
which
then
tells
us record
1
(left- justify)
is
next,
etc.
The
last
entry,
record 3
(right- justify), points us to zero,
which
we
take
to
mean "The
End."
Since
nx$
will
contain an
integer,
we
have
to
first
convert
that
number
to a
two-
byte
string representation,
using
mki$
(line
230
above).
The
following
program
displays the glossary in alphabetical sequence:
300 REM GL0SS0UT/BAS
«
310 CLS
s
CLEAR 300
320 OPEN
"R"
>
1*
"GLOSSARY/BAB"
330 FIELD
1* IB AS
ND$
*
238
AS
MEANING*,
2
AS
NX*
340 INPUT "WHICH RECORD
IS
FIRST ALPHABETICALLY"
5
HI
350 GET
1
t
HI
3S0 PRINT
:
PRINT WD*
370 PRINT MEANING*
380 HI
=
CUI(NX$)
39-0
INPUT "PRESS
<EIMTER> TO
CONTINUE"
5
X
400
IF
HI <>
THEN 350
410 CLOSE
420 END
154