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PL/I allows automatic arrays to be sized dynamically.  The size of an
array can be any expression using variables from a containing lexical
context; for example, you can do:

	declare array_size fixed binary;

	array_size = compute_size();
	begin;
	     declare array (array_size) fixed binary (8);
	     ...
	end;

But you couldn't do this if array and array_size were declared in the
same block.  The one exception to this is arrays in the top-level
block of a procedure, which may be dimensioned using its parameter
variables, e.g.

	my_proc: procedure (array_size);
	     declare array_size fixed binary parameter;
             declare array (array_size) fixed binary (8);
             ...
	end my_proc;

In general, the rule is that the array dimension must be computable
before any local variables are initialized.

Barry Margolin
Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar