Page 21-49
«
→
x
«
IF
‘
x<3
’
THEN
‘
x^2
‘
ELSE
‘
1-x
’
END EVAL
”
Done
”
MSGBOX
»
»
and save it under the name ‘f2’. Press
J
and verify that variable
@@@f2@@@
is
indeed available in your variable menu. Verify the following results:
0
@@@f2@@@
Result: 0
1.2
@@@f2@@@
Result: 1.44
3.5
@@@f2@@@
Result: -2.5
10
@@@f2@@@
Result: -9
These results confirm the correct operation of the IF…THEN…ELSE…END
construct. The program, as written, calculates the function
−
<
=
otherwise
x
x
if
x
x
f
,
1
3
,
)
(
2
2
Note
: For this particular case, a valid alternative would have been to use an
IFTE function of the form: ‘f2(x) = IFTE(x<3,x^2,1-x)’
Nested IF…THEN…ELSE…END constructs
In most computer programming languages where the IF…THEN…ELSE…END
construct is available, the general format used for program presentation is the
following:
IF
logical_statement
THEN
program_statements_if_true
ELSE
program_statements_if_false
END
In designing a calculator program that includes IF constructs, you could start
by writing by hand the pseudo-code for the IF constructs as shown above.
For example, for program
@@@f2@@@
, you could write
IF
x<3
THEN
x
2
ELSE
1-x
END