Initial import.

[pforth] / fth / tut.fth

anew task-tut.fth

: SUM.OF.N.A ( N -- SUM[N] , calculate sum of N integers )
          0  \ starting value of SUM
          BEGIN
              OVER 0>   \ Is N greater than zero?
          WHILE
              OVER +  \ add N to sum
              SWAP 1- SWAP  \ decrement N
          REPEAT
          SWAP DROP  \ get rid on N
      ;

: SUM.OF.N.B  ( N -- SUM[N] )
   0 SWAP  \ starting value of SUM
   1+ 0    \ set indices for DO LOOP
   ?DO     \ safer than DO if N=0
       I +
   LOOP
;

: SUM.OF.N.C  ( N -- SUM[N] )
   0  \ starting value of SUM
   BEGIN   ( -- N' SUM )
       OVER +
       SWAP 1- SWAP
       OVER 0<
   UNTIL
   SWAP DROP
;

: SUM.OF.N.D  ( N -- SUM[N] )
       >R  \ put NUM on return stack
   0  \ starting value of SUM
   BEGIN   ( -- SUM )
       R@ +  \ add num to sum
       R> 1- DUP >R
       0<
   UNTIL
   RDROP  \ get rid of NUM
;

: SUM.OF.N.E  { NUM | SUM -- SUM[N] , use return stack }
   BEGIN  
       NUM +-> SUM \ add NUM to SUM
       -1 +-> NUM  \ decrement NUM
       NUM 0<
   UNTIL
   SUM  \ return SUM
;

: SUM.OF.N.F  ( NUM -- SUM[N] , Gauss' method )
   DUP 1+ * 2/
;


: TTT
       10 0
       DO
               I SUM.OF.N.A .
               I SUM.OF.N.B .
               I SUM.OF.N.C .
               I SUM.OF.N.D .
               I SUM.OF.N.E .
               I SUM.OF.N.F .
               CR
       LOOP
;
TTT