Chapter 101 Shuffling Disk Files - Tandy TRS-80 Owner Manual & Programming Manual

SHUFFLING
DISK
FILES
30 A*
=
STR*(N)
+ "
MONTHS"
40
PRINT "YOU HAVE LIVED ABOUT'
A$
MERGE
"WEEKS/AGE"
with
it
by typing MERGE
"WEEKS/AGE"
(ESTER)
.
Then LIST
the
MERGEd
program.
Notice that
lines 10, 20,
and
30
of the
program you
had
in
memory
were
replaced
by
lines 10, 20,
and
30
of
the
"WEEKS/AGE"
program.
The
line
numbers
tell
the
Computer how
to
merge
the
two programs.
When
there
is
a
conflict
of
line
numbers
(two
line 10s)
f
the
line
from
the disk
file
prevails.
Now
we'll
get technical
(for
those
of
you
who
are
interested).
What
the
Computer
normally
writes
in
your
disk
file is
the
ASCII
code
for
each
char-
acter of data.
For example,
it
writes the
word
AT
with two
codes
—
the
ASCII
code
for
"A"
(65)
and
the
ASCII
code
for
*T"
(84).
(The
ASCII
codes are
all
listed in
Appendix
D).
However,
when
it
SAVEs
a program,
it
writes the
BASIC
words
differently.
To save
space,
it
com-
presses
each
BASIC
word
into
a one-byte "binary"
code.
You
can't
MERGE
a
file
which
contains these
binary
codes.
This
is
why we
had you
type the
A
when
you
SAVEd
the
two programs
above.
The
A
tells
the
Computer
to
write the
ASCII
codes
for
each
BASIC
word
rather
than
the binary
code.
By
checking the
directory,
you can
see
if
the data
in
your
files
are
in
ASCII
or
binary
codes.
If
there
is
an "A"
in
the fourth
column,
it's
all
in
ASCII
codes.
A
"B"
indicates that
some
of the
words
are
in
binary codes.
Note: Try typing
MERGE "MONTHS/AGE"
,
ft
^HTF
ffi.
The
R
tells
the
Computer
to
RUN
the
program
after
it's
MERGEd.
USING
MORE
BUFFER SPACE
When
you
start-up
your disk system,
it
sets
aside
two
buffer areas in
memory
for disk
communica-
tion.
You
can use either or
both
of
them
for
read-
ing or writing
data
to
a disk
file.
Up
to
now,
that's
all
we've used
—
buffers
#1
and
#2. But, as we've
said
earlier,
you can
use
up
to 15
disk buffer
areas.
To use
more
than
2 buffers,
you must
first
reserve
space in
memory
for
them. To do
this,
use the
word
FILES. For example, FILES
3 reserves
3 buffers.
Making
use
of
all
these buffers
will greatly sim-
plify
your programs. For example,
let's
assume
you
own
a
computer
school.
To organize
it,
you
first
put
all
your
students
in
a
file
named "COM-
PUTER/SCHr
Erase memory,
type
and
RUN:
10
OPEN
"0".
*1
.
"C0NPUTER/SCH"
20 FOR
X
=
1
TO
B
30
READ
At
40
PRINT
*1
.
A$
50
NEXT
X
G0
CLOSE
#1
70 DATA JON
i
SCOTT
,
CAROLYN
80
DATA DONNA. BILL
r
BOB
Now
you
can write
this
program
to
assign the
stu-
dents
to
a
BASIC
or
assembly-language
class.
Erase
memory
and
type
this
"Class
Assignment
Program":
I
CLASS ASSIGNMENT
PROGRAM
»l
*Z
»3
10
FILES
3
20 OPEN
"0"
i
30
OPEN
"0"
.
W
OPEN
"I"
50
IF
E0F(3)
G0 INPUT «3.
70 PRINT
80 INPUT
LANGUAGE"!
R
90 IF
R
>
2
THEN
80
100
WRITE
8R
t
ST$
110 GOTO
50
120 CLOSE
8
1
130 CLOSE
82
140
CLOSE 83
"BA5IC/CLS"
"ASSEMBLY/CLS"
"C0MPUTER/SCH"
1
THEN
120
ST4
PRINT ST$
(IS
BASIC
RUN
it.
After assigning
all
the students
to
a
class,
you
can
print a class roster
with
this
program.
Erase
memory,
type,
and
RUN:
54