#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeMap;
    let mut map: BTreeMap<&str, i32> = [
        ("Alice", 0),
        ("Bob", 0),
        ("Carol", 0),
        ("Cheryl", 0),
    ]
        .into();
    for (_, balance) in map.range_mut("B".."Cheryl") {
        *balance += 100;
    }
    for (name, balance) in &map {
        println!("{name} => {balance}");
    }
}