Rust error：expected item, found 'let'

我有一个代码转储，在那里我放了一些Rust 代码的例子，以防我忘记了什么.41+线我一直拿error: expected item, found 'let'分.

我试着改变名字，认为这是名字惯例；但这没用.同样的错误.

这里是垃圾场(实际上还没那么大)

#[allow(dead_code)]


fn main()
{

}





/////////////////////////////////////////tutorial functoins i made

fn if_statements()
{
    //let (x, y) = (5, 10);
    let x = 5;
    let y = if x == 5 { 10 } else { 15 };
        if y == 15 {println!("y = {}", y);}
}



////////////////////////////////////////// tutoiral functions
#[allow(dead_code)]
fn add(a: i32, b: i32) -> i32
{
    a + b

}

#[allow(dead_code)]
fn crash(exception: &str) -> !
{
    panic!("{}", exception);
}


//TUPLES//
let y = (1, "hello");
let x: (i32, &str) = (1, "hello");

//STRUCTS//
struct Point {
    x: i32,
    y: i32,
}

fn structs() {
    let origin = Point { x: 0, y: 0 }; // origin: Point

    println!("The origin is at ({}, {})", origin.x, origin.y);
}

//ENUMS//
enum Character {
    Digit(i32),
    Other,
}

let ten  = Character::Digit(10);
let four = Character::Digit(4);