Reference Guide

RPL Programming 1-15
To enter CASE  END in a program:
1. Press !°%BRCH% !%CASE% to enter CASE … THEN …END…END
2. For each additional test-clause, move the cursor after a test-clause END and press @%CASE% to enter THEN
… END.
Conditional Examples
These examples illustrate conditional structures in programs.
Example: One Conditional Action. The programs below test the value in level 1 — if the value is positive, it’s
made negative. The first program uses a command sequence as the test-clause:
« DUP IF 0 > THEN NEG END »
The value on the stack must be duplicated because the > command removes two arguments from the stack (0. and
the copy of the value made by DUP).
The following version uses an algebraic as the test clause:
« → x « x IF 'x>0' THEN NEG END » »
The following version uses the IFT command:
« DUP 0 > « NEG » IFT »
Example: One Conditional Action. This program multiplies two numbers if both are nonzero.
Program: Comments:
«
→ x y
«
Creates local variables x and y containing
the two numbers from the stack.
IF
Starts the test-clause.
'x‹0'
Tests one of the numbers and leaves a test
result on the stack.
'y‹0'
Tests the other number, leaving another test
result on the stack.
AND
Tests whether both tests were true.
THEN
Ends the test-clause, starts the true-clause.
x y *
Multiplies the two numbers together only if
AND returns true.
END
»
»
Ends the true-clause.
The following program accomplishes the same task as the previous program:
« → x y « IF 'x AND y' THEN x y * END » »
The test-clause 'x AND y' returns “true” if both numbers are nonzero.
The following version uses the IFT command:
« → x y « 'x AND y' 'x*y' IFT » »