Purpose

This is the Forth version of our combination application. It's one of the Palm Samples.

 Requirements

 Source code

Below is the .forth file.

\ combination
\ Palm
\ Quartus Forth

: factorial ( n -- result )
  dup                      \ Stack: n n
  2 < if                   \ if n <= 1
    drop 1 exit            \ return 1
    else dup 1- recurse *  \ recurse
  then
;

: combination ( n p -- result )
  2dup           \ Stack: n p n p
  - factorial    \ n p (n-p)!
  rot factorial  \ p (n-p)! n!
  rot factorial  \ (n-p)! n! p!
  rot            \ n! p! (n-p)!
  *              \ n! (p!*(n-p)!)
  /              \ (n / (p!*(n-p)!))
;

\ Main entry point:
: go ( -- )
  cr
  ." Combination > Palm > Quartus Forth" cr
  cr
  ." factorial(7)=" 7 factorial . cr
  ." factorial(4)=" 4 factorial . cr
  ." factorial(3)=" 3 factorial . cr
  ." combination(7,4)=" 7 4 combination . cr
;

 Comments

Quartus Forth is a mobile tool. As such, it runs directly on your mobile device.

Copy and paste the source code above into a new memo with Palm Desktop. Run HotSync. The source code will be stored in a \Combination memo. Launch Quartus Forth, tap include combination to load the memo. To run the sample, enter go.

The core functions are : factorial, combination and go.

See for yourself how the RPN (Reverse Polish Notation) is amazing and unusual: 7 4 + (post-fixed notation) means 7 + 4 (unfixed notation).

After some practice, it becomes as legible - if not more - than our "traditional" unfixed notation.

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