const THREE_DAYS_IN_SECONDS : u32 = 3 * 24 * 60 * 60;

fn main() {
    println!("
1/ A constant can be defined outside main,
 and be called from main:

---RUNNING THE CODE");
    println!("const THREE_DAYS_IN_SECONDS: {THREE_DAYS_IN_SECONDS}
---END OF EXECUTION");

    println!("
2/ A variable is mutable only if you use mut. Ex:
let mut x = 5;

---RUNNING THE CODE");

    let mut x = 5;
    println!("x (defined by 'let mut') is {x}");
    x = 6;
    println!("x is now {x}
---END OF EXECUTION");


    println!("
3/ Instead of allowing mutability, 
a variable can be 'shadowed'.
It means we redefine a new variable 
on the same namespace. Ex:
let shadow = 7
let shadow = shadow + 3

---RUNNING THE CODE");
    let shadow = 7;
    println!("shadow is {shadow}");
    
    let shadow = shadow +3;
    println!("shadow is {shadow}");

    {
        let shadow = shadow + 10;
        println!("shadow in scope is {shadow}");
    }
        println!("shadow back outside scope is {shadow}
---END OF EXECUTION");

println!("
4/ shadowing even allows to 
change the type of the variable!

---RUNNING THE CODE");
    let secret = "xxxx";
    println!("secret is {secret}");

    let secret = secret.len();
    println!("secret - now defined with secret.len() - 
is now: {secret}
---END OF EXECUTION");
}