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schemedecimalprecision
Devashish Dixit
Devashish Dixit

Reputation: 1193

Scheme : precision of decimal numbers

How can I convert 42.0 to 42.00 in Scheme?
For Example (In Scheme):
When I do (/ 20.00 2), I get 10.0. I want 10.00 as the result of above instead of 10.0

Upvotes: 1

Views: 9014

Answers (4)

user3916579
user3916579

Reputation: 11

If you use racket, I think that could help.

https://docs.racket-lang.org/reference/strings.html#%28def._%28%28lib.racket%2Fformat..rkt%29.~7er%29%29

(~r pi #:precision 4)

"3.1416"

Upvotes: 1

Óscar López
Óscar López

Reputation: 236114

The numbers 10.0 and 10.00 are exactly the same. Maybe you want to format your output to a string with a fixed number of decimals to the right of the dot? try this:

(define (right-pad number len)
  (let* ((nstr (number->string number))
         (diff (- len (string-length nstr)))
         (pads (if (> diff 0) (make-string diff #\0) "")))
    (string-append nstr pads)))

Use it like this:

(display (right-pad (/ 20.00 2) 5))
> 10.00

Notice that the len parameter indicates the total amount of chars desired in the resulting string, including the dot. This solution has the advantage of being independent from external libraries.

Upvotes: 4

Asumu Takikawa
Asumu Takikawa

Reputation: 8523

Óscar's solution works well, but an even easier solution is to use SRFI-48, which provides additional format directives.

(display (format "~0,2F" (/ 20.00 2)))

Upvotes: 7

Matthias Benkard
Matthias Benkard

Reputation: 15769

The objects represented by 10.0 and 10.00 are the same. There is no such thing as a fixed-precision decimal number in R5RS Scheme. What do you need the fixed precision for? If it is relevant for output, you need to do formatted printing of some sort. Check your Scheme implementation's documentation about a printf or format function. If, on the other hand, you actually need decimal arithmetic, you will need to either use exact ratios and round explicitly according to the rules you want to use, or use integers and treat them as units of size 1/100.

Upvotes: 5

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