I was able to turn the string into a char iterator, but I could not figure out how to change elements of said iterator (this can be seen at line 55).

You have a few options here, but the easiest is to collect into a Vec<char>, replace the character there, then do a String::from_iter(chars) to get it back as a string.

You can also manipulate the original chars iterator directly through takes, skips, and so on and collect it into a string, but that's more complicated.

Also, "character" is such a complicated concept because unicode is not simple. If you can work directly with bytes though, you can convert the string to a Vec<u8> (which is the underlying type for String), manipulate that directly, then do String::from_utf8 (or the same method for str) to convert it back to a string.

what is character?

This is simply not possible in rust, because strings are utf-8, so the size of a single character can vary. I think there might be a class for ASCII strings, but otherwise you can just use Vev and then convert to string

Others have already pointed out the issue - in Rust, String is UTF-8 encoded and therefore characters are variable length. So you can't just change a character in a string, as it may not fit (e.g. replacing 'a' with '🙂' would lead to trouble).

You can do what the others suggest, but honestly for a game like hangman, I'd suggest you just work directly with chars and don't use any string. As in, just use a Vec instead of a string. Then you can freely change characters based on index, but this representation uses more memory than a typical String. But this won't matter for your use case.

@cows_are_underrated The simplest way I’ve found to do that is to convert the string into a Vec<char>. UTF-8 strings aren’t optimized for random access because of multi-byte chars.

To array of chars:
let c = s.chars().collect::<Vec<char>>();

And back to string:
let s = c.into_iter().collect::<String>();