Tandy TRS-80 - Page 60

TRIMMING THE FAT OUT OF
DIRECT ACCESS
Now let's
look
at the
"Fielded INPUT
Program:'
Notice
we
used
a FIELD
line. RUN
the
program
without line
20 and see
what
happens
. .
.
Without a
FIELD
line,
the
Computer
does not
know
where
the
two
fields are.
Whenever you
input
FIELDed
records,
use a
FIELD line in
your
input
program.
Can you
guess
what
the
Computer
would do if you
tried
to LSET a
long string,
such
as
"123456789,"
into
one of
the
fields?
LOAD
Program
7,
change
line 30,
and RUN the
program.
(First,
SAVE the
"Fielded
INPUT
Program"
with line 20
reinstated.):
30
LSET A*
=
"lZGaSGTSa"
Now
load
and
RUN
the
"Fielded
INPUT
Program."
A$ is
only 3 bytes.
Therefore,
the
Computer
only
LSETs the
first 3 bytes
of
"123456789."
It chops
the
remaining
characters
off:
^OFFICE
/OA7"
/
Mmm
record
1
record
2
"OFF/C&/
DAT
More on
this
later . . .
Before
going
on
to
the next
program,
try
writing
your own
FIELDed
program:
PROGRAMMING
EXERCISE
#9.1
Write
a direct
access
program
to
put a
mailing
list in a
disk
Hie.
Make
each
record
57 bytes
with
these six
fields:
1. last
name
—
15 bytes
2. first name
—
10 bytes
3.
address
—
15 bytes
4.
city
—
10 bytes
5.
state
—
2 bytes
6. zip code
—
5
bytes
^£3§§§i^
:
.\lVjl ;
.«
"
'
'.-.
:
'
-
PROGRAMMING
EXERCISE
#9.2
Write a
program
to input the
file
you
created
in
Exercise #9.1.
ascs-ffira-afi
A
NUMBER
IS
A NUMBER, .
.
.
Let's
assume
you will be
putting a
lot of
numbers
in
your disk
file.
Every
number
might be a
differ-
ent
length:
-5.237632 31
673285
However, it is
very
important
that the
Computer
not chop
any of
the digits
off. This
might
entirely
change the
number's
value.
The word
MKN$
will
solve this
problem:
PROGRAM
8
20
bytes
10 OPEN "D"
t
»1
p
"OFFICE/DAT"
t
10
20 FIELD
*l t 5 AS
A*
, 5
AS Bt
30 LSET
ft*
=
MKNt<5)
40 LSET
B*
=
"PEN"
50
PUT
*1
p 1
60 LSET At
=
MKN$t-iG)
70
LSET
Bt
=
"PAPER"
80
PUT
*1
> 2
90
CLOSE
»1
The only
difference
between
this
program
and
pro-
gram 7 is
lines
10, 20, 30,
and 60.
This is what
it
stores
in your disk
file:
50