Tandy TRS-80 Owner Manual & Programming Manual page 40

CHANGING
IT
ALL
AROUND
SO IF
X*
=
""
THEN X$
=
90
WRITE
*1
i
X*
A$
RUN
the
program.
As
soon as the
Computer
gets
to line 90,
it
prints:
?FM
ERROR
IN
90
LIST
the
program. Line 10 opens buffer
#1
to
input data.
Line
90,
however,
is
attempting
to out-
put data
to
buffer
#1.
The Computer
won't output
data
to
a buffer
opened
for input.
This
is
where the additional buffer
becomes
handy. To output
your changed data
to
the
disk,
you can open another
buffer for
output.
Add
these
lines:
15
OPEN
"0"
.
*2, "NEW/DAT"
90
WRITE
»2* X*
120
CLOSE »2
RUN
the
program.
Change
"COW"
to
"GIRAFFE"
This
is
the
way
the entire
program
looks:
10
OPEN "I". «1
.
"ANIMALS/DAT"
15
OPEN
"0"
.
«2. "NEW/DAT"
20
IF
EOFt
1) =
-1
THEN
110
30 INPUT
81
,
A*
40 CLS
:
PRINT
@
10E,
"DATA ITEM
:" A$
50 PRINT
@
451. "PRESS <ENTER>
IF
NO
CHANGE"
;
S0 PRINT
@
2G3» "CHANGE
:
"
i
70
INPUT X*
B0 IF X$
=
""
THEN X*
=
A*
90
WRITE 82. K$
100
GOTO 20
110
CLOSE
»1
120
CLOSE *2
Line 10
OPENs
communication
to
buffer
#1
for
input
from a disk
file
named "ANIMALS/DAT."
Line
15
OPENs
communication
to
buffer
#2
for
output
to
a disk
file
named "NEW/DAT:
7
Line 30
inputs
A$
from
buffer
#1. Line 70 allows
you
to
INPUT
X|,
which
will replace
A$.
If
you
input X$,
line
90
outputs
it.
Line 90
outputs
X$
to
buffer
#2, which,
in
turn,
WRITEs
it
to
"NEW/
DAT!'
Line 110
CLOSEs
communication
to
buffer
#1
and
line
120
CLOSEs
communication
to
#2.
Now
you have two
files.
"ANIMALS/DAT"
con-
tains
the
old
data
and
"NEW/DAT"
contains the
new.
Add
these
lines to
the
program and
RUN
it:
130
KILL "ANIMALS/DAT"
140
RENAME "NEW/DAT"
TO
"ANIMALS/DAT"
Now
the
old
"ANIMALS/DAT"
file is
deleted
from
the disk
and
the
"NEW/DAT"
file
has been
renamed
to
"ANIMALS/DAT."
To see
what
this
updated
file
contains,
SAVE
this
program
if
you
want, erase
memory, and
type
and
RUN:
10
OPEN
"I") 81
,
"ANIMALS/DAT"
20
IF
E0F(1)
=
-1
THEN B0
30 INPUT
81
,
A$
40
PRINT
A*
50
GOTO
20
G0 CLOSE
«1
Understand? Try
these
exercises:
PROGRAMMING
EXERCISE
#0.1
Write a
program
which
will
allow
you
to
add
animals
to
"ANIMALS/
DAT'
Hint
—
You
must add them
to
the
end
of
the
file.
PROGRAMMING
EXERCISE
#6.2
Write a
program
which
will
allow
you
to
delete
animals from "ANI-
MALS/DATT'
Ready
for
the big
time?
Our
next
exercise
is
a pro-
gram many
of
you
will
want
—
a mailing
list
pro-
gram.
We'll start
you out with these
lines
which
input the
names,
addresses,
and phone numbers
of
your
club
members:
30