Apple IIe - Page 54

54
Apple
lie
Users
Handbook
A
DIM
statement
should
appear
in a
program
before
the
array
variable
it
is
dimensioning
appears
.
If
an
array
variable
is
used
in
a
program
before
it
is
dimensioned
,
the
Bad
Subscript
error
may
occur.
An array
can
also
consist
of
two
dimensions.
Such
an
array
is
known
as a
two-dimensional
array (or
table). An
example
of
an
array
of
4 rows
and
3
columns
is
shown
in Illustration
3-2.
A
two-dimensional
array
contains
two
subscripts.
The
first
subscript
contains
the
row
location
,
while
the
second
subscript
contains
the
column
location
.
The
subscripted
variable A(1,0)
identifies
the
darkened
area
in
the
array
shown
in
Illustration
3-2.
Illustration
3-2.
Two-Dimensional
Array
Columns
0
1
2
0
1
Rows
2
3
Expressions and Operators
The
values
of
variables
and
constants
are
combined
to
form
a
new
value
through
the
use
of
expressions.
The
following
are
examples
of
expressions
.
4+7
A$+
B$
3*2
14<21
XANDY
Applesoft
BASIC
includes
several
types
of
expressions
including
arithmetic, relational,
and
Boolean.
In
our
previous
examples,
the
first
three
examples
are
arithmetic
expressions
,
while
the