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Фрагмент инструкции
Implicit
declaration
of
v
ariables
according
to
the
standard
HP
Declare
All
V
ariables
F
OR
TRAN
77
con
v
en
tions
(v
ariables
b eginning
with
the
letters
I
through
N
are
INTEGER;
the
rest
are
REAL)
causes
a
default
data
item's
size
to
b e
assigned.
In
addition,
implicit
declarations
are
not
do cumen
ted,
making
mo
dications
dicult.
Although
implicit
declarations
might
sa
v
e
programming
time
during
the
initial
writing
phase,
it
might
take
more
time
for
debugging
and
mo
difying
the
program.
Therefore,
declaring
all
v
ariables
in
a
program
should
sa
v
e
programming
time,
as
w
ell
as
ensuring
the
in
tegrit
y
of
the
data
structures.
Because
HP
F
OR
TRAN
77
has
an
implicit
declaration
facility
dened
as
part
of
the
ANSI
language,
y
ou
might
forget
to
declare
all
v
ariables.
F
or
example,
it
w
ould
b e
easy
to
forget
to
declare
an
index
of
a
DO
lo
op
if
the
lo
op
w
as
added
after
the
initial
design
w
as
complete.
Y
ou
can
use
the
IMPLICIT
NONE
statement
to
turn
o
the
implicit
declaration
facilit
y
.
The
IMPLICIT
NONE
statement
(a
MIL-STD-1753
extension)
generates
error
messages
for
undeclared
v
ariables.
Placing
this
statement
in
eac
h
program
unit
immediately
follo wing
the
PR
OGRAM,
SUBR
OUTINE,
FUNCTION,
or
BLOCK
D
A
T
A
statement
guarantees
that
no
v
ariable
declaration
is
o
v
erlo
ok
ed.
Data
alignment
requiremen
ts
dier
b et
w
een
systems.
F
or
example,
Av
oid
Using
the
nonc
haracter
data
on
some
mac
hines
m
ust
b e
w
ord-aligned,
while
EQUIV
ALENCE
c
haracter
data
on
other
mac
hines
m
ust
b e
aligned
on
a
b
yte
Statement
b oundary
.
Considering
the
dieren
t
mac
hine
w
ord
sizes
b et
w
een
systems,
y
ou
can
see
ho
w
data
alignmen
t
and
equiv
alence
o
v
erlapping
could
c
hange
without
b eing
noticed
when
a
program
is
p orted
b et
w
een
systems.
Therefore,
when
p ossible,
a
v
oid
equiv
alences
b et
w
een
c
haracter
and
nonc
haracter
data.
Because
systems
store
data
dieren
tly
,
an
EQUIV
ALENCE
statement
can
cause
storage
allo
cation
problems.
Complicated
equiv
alence
expressions
ha
v
e
a
higher
c
hance
of
problems
in
the
storage
allo cation
algorithm;
therefore,
do
not
try
to
conserv
e
storage
b
y
using
equiv
alences.
Also,
long
and
complicated
equiv
alence
expressions
can
b e
confusing
when
c
hanges
ha
v
e
to
b e
made
to
the
program.
Because
common
blo
c
ks
are
implemen
ted
dieren
tly
on
dieren
t
HP
Declare
Common
systems,
y
ou
should
declare
eac
h
common
blo
c
k
exactly
the
same
in
Blocks
the
Same
in
ev
ery
program
unit
in
whic
h
it
is
used.
By
doing
this,
y
our
program
Ev
ery
Program
Unit
is
easier
to
read
and
is
consisten
t
in
data
storage.
If
common
blo
c
ks
are
not
declared
the
same,
some
of
the
same
problems
asso
ciated
with
the
EQUIV
ALENCE
statement
could
o ccur.
Ho
w
ev
er,
b ecause
the
declarations
are
in
dieren
t
program
units
(and
p ossibly
in
dieren
t
les),
the
problems
are
more
dicult
to
nd
and
correct.
T
o
ensure
that
the
declarations
remain
iden
tical,
use
the
INCLUDE
statement
or
INCLUDE
compiler
directive.
Place
eac
h
common
blo
c
k
declaration
and
asso
ciated
v
ariable
declarations
in
a
separate
le;
Programming
for
P
ortability
7-5
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