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pps #27
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2022-08-26
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PEEKs, POKEs, AND SYSes -- Part 27
-- continued from Part 26 --
Arrays start at VARTAB and end at
STREND. Before you dimension your
first array, VARTAB and STREND both
point to the same location -- the end
of simple arrays. Each time you use a
new BASIC array, it gets built at
STREND, and then STREND is changed to
point to the end of that new array.
There's really no way to explain the
structure of arrays without resorting
to charts, so here they come!!! Note
well that the arrays start at the
TOP of the chart, and as you read down
the memory addresses get higher. This
is the reverse of the convention I
have been using. If the meaning of
the chart isn't immediately clear to
you, try reading the explanations that
follow it.
ARYTAB points to the beginning of
the first array. All arrays are
organized like this:
A. Two bytes for the name
B. Two bytes for an index to the
next variable name.
C. One byte to tell how many
dimensions.
D. Two bytes for each dimension to
tell how many elements each
dimension has
E. The actual array variables
Every array has these five areas,
as charted below:
======================================
CHART 2:
What arrays look like in general.
--------------------------------------
purpose of area size of area
+----------+
A !name ! always 2 bytes
+----------+
B !offset to ! always 2 bytes
!next array!
!name !
+----------+
C !number of ! always 1 byte
!dimensions!
+----------+
D !sizes of ! always 2 bytes per
!dimensions! dimension
+----------+
E !variables ! size varies with
! ! variable type and
+----------+ size of dimensions
======================================
-------< continued in Part 28 >-------