Hi, I’m looking at converting numeric characters to integers i.e. #\1 to 1 (not 49 which is the character code) I have not seen a standard function for this so I have tried 2 alternative appraches to this (define (char->int c) (- (char->integer c) 48)) and (define (char->int c) (string->number (~a c))) is one of these methods the ‘preferred’ way, or is there another way?

@mark.warren (string->number) I think

Does that work on single characters

I don’t think so, but you can make a string out of one character

That’s what (~a c) does

(string->number (string #\1))

Yeah, that’s what my second approach does, but using ~a instead of string

Yes. It’s not that frequent to need exactly one character as an integer, so I guess any of those approaches are good. The only thing would be about performance if it goes into a really tight loop or something.

@mark.warren the first one is the way it’s usually done

@samth Thanks, I’m just doing a checksum test on a numeric string, the check it’s very basic but it needs you to multiply each digit of the number by a weight and then sum them.

I knew it :smile:

I was trying to find some usecase, and this is exactly what came to my mind first :stuck_out_tongue:

@jerome.martin.dev Hehe

I think you can also do that with a (for) loop … something like (in-char)

nope, (in-string)

Yeah, that’s how I’m doing it, I do a string->list on the string which gives me the characters, which I then needed to convert to integer values.

(define (char->int c) (- (char->integer c) 48)) (define (check-remainder check-number) (modulo (for/sum ([weight (range 10 1 -1)] [digit (string->list check-number)]) (* weight (char->int digit))) 11))

what I mean is that you can probably make a one-liner: (for/sum ([c (in-string "1234")]) (- (char->integer c) 48))

oh yeah, right

you used that :stuck_out_tongue:

nevermind my comment then, I was too slow!

so yeah the only difference is that I use (in-string) instead of (string->list) which has an optimization in the for loop

Thanks for the help

@jerome.martin.dev I’ll give the in-string way a go

@mark.warren if the indended use is for byte streams, how about using bytes directly?

@shu—hung It is an input from a user, so it’s a string, I could convert it to a byte string.