HP HP-28S - Page 279

Techniques:
• List of variables. DOWN uses VARS to return the list of variables
and subdirectories in the current directory.
• Error trap. To check whether a name in the VARS list is a directory,
DOWN uses the name as an argument to RCL; since directories
can't be recalled to the stack, an error occurs if the name is a direc-
tory
name, and the name is added to the list of directory names.
Program
::~.
' • ..'AR:3
"* './
. ::::
::::"
v SIZE
FOF: .j
v .j GET
I FERR F.:CL DROP
THEt~ +
END
~lDn
t'lnW
I ENTER I
~ DOWN ISTol
Comments
Begin the program.
Put on the stack a list of the
names of all variables and
subdirectories.
Store
the VARS list in a local
variable
v.
Begin the defining program .
Put the list of directory names on
the stack (initally empty).
Put 1 and size of v on the stack.
For
each name in v, do the
following:
Get the name.
Attempt to recall the contents of
a variable with that name; if suc-
cessful,
drop the contents.
If RCL caused an error, the name
must be a directory name, so add
the name to the list of directory
names.
End of the THEN clause and the
program structure.
Repeat for next
name in v.
Create a custom menu for the di-
rectory names.
End the defining program.
End the program.
Put the program on the stack.
Store
the program as DOWN.
278 28: Programming Examples