ocaml looking at a specific digit of an int

Question

I am writing an ocaml program and I can't figure out how to look at specific digits of an int

so say for example we have

let a = 405;;

I want to be able to look at the first digit, 4, or the second one, 0. How can I accomplish this? I was thinking of turning it into a string and looking at the chars, but I feel like there should be another way of doing it.

Answer 1

You can write a recursive function to extract all digits from a number:

(* Assuming n is a non-negative number *)
let digits n =
    let rec loop n acc =
        if n = 0 then acc
        else loop (n/10) (n mod 10::acc) in
    match n with
    | 0 -> [0]
    | _ -> loop n []

Once you have a list of digits

# digits 405;;
- : int list = [4; 0; 5]

you can get any digit by using some List functions.