HP 48gII Graphing Names Check List for Exactly Two Names, Techniques used in Names, `Onames K

NAMES (Check List for Exactly Two Names)

If the argument for a program is a list (as determined by VFY), NAMES verifies that the list contains exactly two names. If the list does not contain exactly two names, an error message appears in the status area and program execution is aborted.

Level 1	→	Level 1
{ valid list }	→
{ invalid list }	→	(error message in status area)

Techniques used in NAMES

Nested conditionals. The outer conditional verifies that there are two objects in the list. If so, the inner conditional verifies that both objects are names.

Logical functions. NAMES uses the AND command in the inner conditional to determine if both objects are names, and the NOT command to display the error message if they are not both names.

NAMES program listing

Program:	Comments:
«
IF	Starts the outer conditional structure.
OBJ→	Returns the n objects in the list to levels
	2 through (n + 1), and returns the list
	size n to level 1.
DUP 2. SAME	Copies the list size and tests if it’s 2.
THEN	If the size is 2, moves the objects to
DROP	level 1 and 2, and starts the inner
IF	conditional structure.
TYPE 6. SAME	Tests if the object is a name: returns 1 if
	so, otherwise 0.
SWAP TYPE 6. SAME	Moves the second object to level 1, then
	tests if it is a name (returns 1 or 0).
AND	Combines test results: Returns 1 if both
	tests were true, otherwise returns 0.
NOT	Reverses the final test result.
THEN	If the objects are not both names,
"List needs two names"	displays an error message and aborts
DOERR	execution.
END	Ends the inner conditional structure.
ELSE	If the list size is not 2, drops the list size,
DROPN	displays an error message, and aborts
"Illegal list size"	execution.
DOERR
END	Ends the outer conditional.
»
`ONAMES K	Stores the program in NAMES.
	RPL Programming Examples 225