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Language Elements
2-8
If
a variable
is
referenced before it has been assigned a value, its value
is
zero. The
NEW,
RUN, CLEAR, LOAD, and MERGE instructions set all variables to zero.
Individual variables can be specified by individual type identifier suffixes, which
override group type identifiers used to specify blocks
of
variables. Table
2-5
shows
these suffixes.
Blocks
of
variables beginning with specific characters can be specified as integer,
single-precision,
or
double-precision with the DEFINT, DEFSNG, and DEFDBL
statements. The general form of these statements is: DEFxxx m[-n], where n
is
any
letter A through Z,
and
m
is
any letter A through Z that precedes n in the alphabet,
(Le., the block L-Q
is
legal, but Q-L
is
not). In this way, all variables beginning with
a certain letter or letters may be defined as one type.
The variable default type
is
single precision, as if a DEFSNG A-Z had been executed
at the start
of
a given program.
If
certain variables should be of another type, you
should define them
at
the start
of
the program to prevent errors. In all cases, the
type identifiers
(%
for
integer,!
for single-precision, and I for double-precision)
override any variable block type assignment.
Note that A$,
AOJo,
A!, and
AI
are four different variables.
If
the default variable
type for variables beginning with the letter A
is
single precision, then A and
A!
are
the same variable.
To economize on memory space and execution time, you should use integer
representation rather
than
single-precision representation,
and
single-precision
rather
than
double-precision, when this
is
possible.
String Data
BASIC-80 accepts strings
of
characters as data. Like numeric values, strings can be
either constants or variables.
String Constants
A string constant
is
a group
of
characters, enclosed in quotation marks. Quotation
marks cannot be used within string constants. String constants can be up to
255
characters long. Some string constants are:
"This
is a string
constant."
"48, 23H, 373799"
String Variables
String variables are string values which can change during program execution. A
string variable name
is
one or more characters, the first
of
which must be a letter,
followed by
$.
If
more
than
two characters are entered as a variable name, onlv the
first two are read.
String variables can contain strings
of
from 0-255 characters. When you first invoke
BASIC-80, however, there
is
only storage space for 100 characters. The CLEAR
command must
be
used to increase the amount of available string space. Here are
some examples of assignments to
strip.g variables:
A$
=
"Enter
next data
string"
B$
=
"40
* 1. 7234E +
3"
NAMES$ =
"Warren,
Mark, Evan"
BASIC-80