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SECTION 4
aSING BASIC
COMMANDS WITH
DOS 2.5
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BASIC Commands Used With DOS
Before learning about
the
BASIC commands
used
with
DOS
2.5
,
you need to know
how the
commands will
act
on programs being
stored and
retrieved
.
The
following
paragra
phs explain the two
types
of files that can contain
BASIC
programs.
Tokenized and Untokenized Files
The
first
type
of file
,
called
"
untokenized
,"
contains standard
ATASCll
lexl
characters,
so it looks like a printout of a
BASIC
program
.
These
programs
do not
retain their
symbol tables each
lime
they are loaded and saved
.
The
symbol table associates the
variable
name
with the
memory
location where the values for that
variable are stored
.
To
store and
retrieve
a
file
in its
untokenized
form
,
you use the LIST and ENTER
commands.
A
lokenized file
is a condensed version of a
BASIC
program
.
II
has one-byte
tokens instead
of the ATASCIl characters
to
repre-
sent the
BASIC
commands.
You can
move
tokenized programs
back and forth between the
disk
drive and computer memory
using the SAVE and LOAD commands
.
Tokenized
versions of a
file
are generally shorter and load faster than untokenized
ver-
sions.
For
this reason
,
many programmers prefer
to
store their
programs
in
the tokenized form.
Usually
during program development the symbol table becomes
cluttered with unused variable names
.
If
you use a variable
in
a
program line and then change the variable
name
or
delete
the
line
,
the
original variable name remains in
the
symbol
table.
Use
the
following procedure to clear the symbol of all
unused names
.
63
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