HP 39g Graphing Calculator - Manual (Page 226)

IF... THEN... Executes the true-clause sequence of commands if the test-
ELSE... END clause is true, or thefalse-clause sequence of commands if the
test-clause is false.
IF test-clause
THEN true-clause ELSE false-clause END
Example
l^A :
IF A==l
THEN MSGBOX A
ELSE MSGBOX A
END
EQUALS 1" :
IS NOT EQUAL TO 1
CASE...END Executes a series of test-clause commands that execute the
appropriate true-clause sequence of commands. Its syntax is:
CASE
IF test-clause I THEN true-clause i END
IF test-clause
2
THEN true-clause
2
END
IFERR.
THEN..
END...
IF test-clause^ THEN true-clause,^ END
END
When CASE is executed, test-clause^ is evaluated. If the test
is true, true-clause^ is executed, and execution skips to END.
If test-clauseif false, execution proceeds to test-clause
2
-
Execution with the CASE structure continues until a true-
clause is executed (or until all the test-clauses evaluate to
false).
Many conditions are automatically recognized by the HP
39G/40G as error conditions and are automatically treated as
errors in programs.
IFERR...THEN...END allows a program to intercept error
conditions that otherwise would cause the program to abort.
Its syntax is:
IFERR trap-clause
THEN error-clause END
15-18 Programming