You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: brockar.rs
    path of file: ./repos/roadmap-retos-programacion/Roadmap/07 - PILAS Y COLAS/rust
    
    the code of the file until where you have to start completion: use std::io;
fn main() {
    let mut array: Vec<i32> = vec![1, 2, 3];
    println!("pila: {:?}", array);
    pila_agregar(&mut array, 4);
    println!("pila_agregar, (4): {:?}", array);

    println!(
        "pila_quitar, quita {}, la pila queda: {:?}",
        pila_quitar(&mut array),
        array
    );

    println!("cola: {:?}", array);
    cola_agregar(&mut array, 5);
    println!("cola_agregar, (5): {:?}", array);

    let ultimo_valor = cola_quitar(&mut array);
    println!(
        "cola_quitar, quita {}, la cola queda: {:?}",
        ultimo_valor, array
    );

    println!("Presiona Enter para empezar con las funciones extras");
    let mut input = String::new();
    io::stdin().read_line(&mut input).expect("Error de lectura");
    clear_terminal().expect("Error al limpiar");
    extra1();
    extra2();
}

fn pila_agregar(vector: &mut Vec<i32>, add: i32) {
    vector.push(add);
}

fn pila_quitar(vector: &mut Vec<i32
    
fn extra2() {
    clear_terminal().expect("Error al limpiar");
    let mut cola: Vec<String> = Vec::new();

    loop {
        println!("-----------");
        println!("| EXTRA 2 |");
        println!("-----------");
        println!("\"imprimir\" para imprimir\n\"papel\" para agregar un papel a la cola de impresion\n\"salir\" para cerrar el programa");
        let mut entrada: String = String::new();
        std::io::stdin().read_line(&mut entrada).unwrap();
        entrada = entrada.trim().to_string();
        if entrada == "imprimir" {
            if !cola.is_empty() {
                clear_terminal().expect("Error al limpiar");
                println!("Imprimiendo...");
                println!("{}", cola_quitar_s(&mut cola));
            } else {
                clear_terminal().expect("Error al limpiar");
                println!("No hay papeles");
            }
        } else if entrada == "salir" {
            break;
        } else {
            cola_agregar_s(&mut cola, entrada);
            clear_terminal().expect("Error al limpiar");
        }
    }
}