To lower, to upper case

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examples/strings/to-lower-to-upper/src/main.rs

fn main() {
    let text = "The Green cat";
    println!("{}", text);
    println!("{}", text.to_lowercase());             // on &str
    println!("{}", text.to_string().to_lowercase()); // on String

    println!("{}", text.to_uppercase());             // on &str
}

The Green cat
the green cat
the green cat
THE GREEN CAT