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RPN Power 48 manual · Chapter 15 of 19

Programming

Write programs between the program brackets, use local variables and the control structures, and run them from the VAR menu.

15.1What a program is#

A program is an object written between « and ». It holds a sequence of objects and commands that run when you evaluate it. Left shift 7 types the brackets. Commands you press inside a program are typed as words instead of being run. Store the program in a variable and it becomes a new command that you run from the VAR menu.

Example 15.1

Type a program

  1. Left shift 7, then 2 and the multiply key.

    ◀« »72×ENTER
Result of the example "Type a program" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: « 2 * ».
You should see« 2 * »
Example 15.2

Store and run a program

  1. Type the program « 2 * » and store it in a variable called dbl.

    ◀« »72×ENTER'αα◀F4◀F2◀PREVNXTαENTERSTO▶

  2. Type 21 and press the dbl soft key in VAR.

    21VARF1
Result of the example "Store and run a program" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 42 / dbl .
You should see1: 42

See also Write a program in RPL

15.2A program that works on the stack#

Example 15.3

Square a number

  1. Type « DUP * »: left shift 7, then DUP from the STACK menu, then multiply.

    ◀« »7◀STACKTOOLF1×ENTER

  2. Store it in a variable called sqr.

    'αα◀ATANTAN◀ASINSIN◀ACOSCOSαENTERSTO▶

  3. Run it on 5.

    5VARF1
Result of the example "Square a number" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 25 / sqr .
You should see1: 25

15.3Local variables with the arrow#

The arrow (left shift ENTER) at the start of a program takes values from the stack into local names. Inside the inner program the names hold the values. This is how you write formulas in a readable way.

c=a2+b2c=\sqrt{a^{2}+b^{2}}
Example 15.4

Hypotenuse program

  1. Type « → a b « a SQ b SQ + √ » » and store it as hyp.

    ◀« »7◀→ENTERαα◀F1αSPCαα◀F2αSPC◀« »7αα◀F1α◀√xSPCαα◀F2α◀√x+√xENTER'αα◀PRGMODE◀ABS×◀x²√xαENTERSTO▶
    After step 1: Type « → a b « a SQ b SQ + √ » » and store it as hyp. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / hyp .

  2. Run it with legs 3 and 4.

    3ENTER4VARF1
Result of the example "Hypotenuse program" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 5 / hyp .
You should see1: 5

15.4The PRG menu#

Left shift MODE opens PRG with the structure words. Pressing one inside a program types the word with spaces around it.

PRG page 1. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / «» IF THEN ELSE END CASE .
PRG page 1.
PRG page 2. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / FOR NEXT STEP STARTWHILE REPEA.
PRG page 2.
PRG page 3. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / DO UNTIL → IFERR EVAL IFTE .
PRG page 3.
PRG page 4. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / IFT ERRM ERRN ERR0 DOERR TYPE .
PRG page 4.
WordsMeaning
«»A pair of program brackets.
IF THEN ELSE ENDDo something only if a test is true.
CASEA multi-way choice.
FOR NEXT STEPA counting loop with a named counter.
START NEXTA counting loop with no named counter.
WHILE REPEAT ENDRepeat while a test is true.
DO UNTIL ENDRepeat until a test is true.
→Create local variables.
IFERRRun code and catch an error.
EVAL, IFTE, IFTEvaluate; choose a value by a test; run if a test is true.
ERRM, ERRN, ERR0, DOERRError message, number, clear it, raise one.
TYPEThe kind of object.

15.5Decisions with IF#

IF test THEN true-part ELSE false-part END. The test leaves 1 (true) or 0 (false) on the stack.

Example 15.5

Absolute value program

  1. Type « → x « IF x 0 < THEN x NEG ELSE x END » » and store it as absv.

    ◀« »7◀→ENTERαα◀1/x÷α◀7◀PRGMODEF2αα◀1/x÷αSPC0SPC◀<4SPC◀PRGMODEF3SPCαα◀1/x÷αSPC▶NEG−SPC◀PRGMODEF4SPCαα◀1/x÷αSPC◀PRGMODEF5ENTER'αα◀F1◀F2◀ATANTAN◀#EEXαENTERSTO▶
    After step 1: Type « → x « IF x 0 < THEN x NEG ELSE x END » » and store it as absv. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / «» IF THEN ELSE END CASE .

  2. Run it on −5.

    5+/−VARF1
Result of the example "Absolute value program" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 5 / absv .
You should see1: 5

15.6Loops with FOR and NEXT#

FOR takes a start and an end from the stack and runs the body once for each value of its named counter. The program below sums the numbers from 1 to n.

∑k=1nk\sum_{k=1}^{n}k
Example 15.6

Sum 1 to 10

∑k=110k=55\sum_{k=1}^{10}k=55

  1. Type « → n « 0 1 n FOR k k + NEXT » » and store it as sumn.

    ◀« »7◀→ENTERαα◀→NUMEVALα◀70SPC1SPCαα◀→NUMEVALα◀MODENXTF1αα◀RCLSTO▶αSPCαα◀RCLSTO▶αSPC+SPC◀PRGMODENXTF2ENTER'αα◀ATANTAN◀=+/−◀UNDOHIST◀→NUMEVALαENTERSTO▶
    After step 1: Type « → n « 0 1 n FOR k k + NEXT » » and store it as sumn. The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: / FOR NEXT STEP STARTWHILE REPEA.

  2. Run it with 10.

    10VARF1
Result of the example "Sum 1 to 10" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 55 / sumn .
You should see1: 55

15.7START, WHILE, DO and CASE#

START n m … NEXT repeats without a counter name. WHILE test REPEAT body END tests first; DO body UNTIL test END tests after. CASE test THEN action END … END chooses the first true branch. IFTE takes a test and two values and returns one of them; IFT runs the next object only when the test is true.

Example 15.7

Choose a value with IFTE

  1. Push the test 1, then two values, then IFTE (PRG page 3, sixth key): the first value is chosen.

    1ENTER10ENTER20ENTER◀PRGMODENXTNXTF6
Result of the example "Choose a value with IFTE" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 10 / DO UNTIL → IFERR EVAL IFTE .
You should see1: 10
Example 15.8

Use IFT

  1. Push test 1, a value 99, press IFT (page 4, first key).

    1ENTER99ENTER◀PRGMODENXTNXTNXTF1
Result of the example "Use IFT" The display shows: RAD { HOME } / 6: / 5: / 4: / 3: / 2: / 1: 99 / IFT ERRM ERRN ERR0 DOERR TYPE .
You should see1: 99

15.8Catch errors with IFERR#

IFERR body THEN handler END runs the handler if the body causes an error. ERRM returns the message text of the last error, ERRN its number, and ERR0 clears it. DOERR raises an error of your own.

15.9Read and paste a program listing#

Programs are plain RPL text, for example:

  • « DUP * »
  • « → a b « a SQ b SQ + √ » »

The Data and programs sheet lists the programs stored in variables and lets you copy them as text or load a program from text.

See also Import and export programs

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