From racket-users  Sat Oct 15 20:03:39 2005
From: jmarshall () alum ! mit ! edu (Joe Marshall)
Date: Sat, 15 Oct 2005 20:03:39 +0000
To: racket-users
Subject: [plt-scheme] Printing
Message-Id: <c948168d0510151303p200a6810o33675d1ebc29f6d1 () mail ! gmail ! com>
X-MARC-Message: https://marc.info/?l=racket-users&m=139305339514946

As it happens, I wanted to do this last week.
Here is my solution:

(define (format-float float digits)
  (let* ((numerals (number->string (round (* (inexact->exact float)
(expt 10 digits)))))
         (length   (string-length numerals))
         (dot      (- length digits)))
    (string-append

     (if (< dot 0) "0" (substring numerals 0 dot))
     "."
     (if (< dot 0)
         (string-append (make-string (- dot) #\0) numerals)
         (substring numerals dot length)))))


On 10/15/05, Chongkai Zhu <mathematica at citiz.net> wrote:
> You could also try SRFI-48. I have already port it into
> PLT Scheme. The code is now available from Schematics CVS.
> One reason it is not in PLT now is that when doing the
> port, I find several bugs in the reference implementation.
> Although these bugs are fixed now, maybe there will be other
> bugs. Should I insert the existin code into PLT?
>
> Chongkai
>
> >This is a really simple question, but I can't find the answer anywhere (help-desk, google, etc.).  How do you control, how many decimal places get printed with a floating pointer number.
> >
> >For example I want somthing like:
> >
> >(define PI 3.1479)
> >
> >(printf "~1.2a\n" PI) => 3.14
> >
> > or
> >
> >(printf "~a\n" (decimal-places PI 2)) => 3.14
> >
> >
> >Thanks,
> >
> >Evan
> >
>
>
>
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>


--
~jrm