Pig Latin Application in rust
Some small remarks:

according to the documentation, you want to output irst-fay on first, but your code will output irstf-ay instead

your code will only work on lower case words, but not on &quot;Apple&quot;

instead of print!(&quot;{} &quot;, format!(...)) use print!(...)

instead of nth(0) use next()

I recommend you to format your code with rustfmt

instead of &amp;word[word.chars().next().unwrap().len_utf8()..] you can use c.len_utf8() if you name your match instead of using _, e.g.
match word.chars().nth(0).unwrap() {
     'a' | 'e' | 'i' | 'o' | 'u' | 'y' =&gt; print!(&quot;{}-hay &quot;, word.trim())),
      c =&gt; print!(&quot;{}-{}ay &quot;, &amp;word[c.len_utf8()..].trim(), c),
};


if you know that your index will end up at a proper UTF8 boundary you can use &amp;word[1..] and &amp;word[..1] instead of your indexing, but your variant is a lot safer. Well done here, as invalid string slicing is a common error in first Rust experiences :)