Member Avatar for lotrsimp12345

I can write the recursion version correctly need help with writing a do loop in DrScheme.

After the do loop the variable x is sent to car L intially and then is updated to first element of everything but first element in list.

(define (sumiteration L)
  (do ((x (car L) (car(cdr L))))
    ((null? L))
    (set! sum (+ sum x)))
)
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The do form needs two parts: a list of loop bindings (each as (var init step)), and a termination clause that returns the final result. The original attempt used (car L) as an init for x (that will blow up when L is empty because in do inits are evaluated before the termination test). was on the right track: initialize an accumulator to 0 and advance a list variable each loop — just fix the typo (suma) and provide the missing binding.

A simple, clear do version that avoids mutating the original argument:

(define (sumiteration L)
  (do ((total 0)
       (rest L (cdr rest)))
      ((null? rest) total)
    (set! total (+ total (car rest)))))

How it works: total starts at 0; rest starts as the input L. Before each iteration Scheme checks ((null? rest) total); if true it returns total. Inside the body car is safe because rest is known non-empty; after the body rest is updated to (cdr rest) for the next iteration. This keeps the loop local and readable — prefer a fresh rest name instead of changing the function argument L. If do is not recognized in your DrScheme language level, switch to an R5RS/Racket language level or use a simple recursion or fold alternative.

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Member Avatar for jonsca

Did you mean to post this in CompSci?

Member Avatar for lotrsimp12345

yea my bad.

Member Avatar for WaltP

Moved...

Member Avatar for lotrsimp12345

delete one of the threads since i posted it here. doesn't matter which one.

Member Avatar for lotrsimp12345

some one please help I am really confused!! :(

Member Avatar for davibq

(define (sumiteration L)
(do ((sum 0)
)
((null? L) suma)
(set! sum (+ sum (car L)))
(set! L (cdr L))
)
)

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