How to print structs and arrays?

As mdup says, you can use Debug, but you can also use the Display trait.

All types can derive (automatically create) the fmt::Debug implementation as #[derive(Debug)], but fmt::Display must be manually implemented.

You can create a custom output:

struct MyStruct {
    a: i32,
    b: i32
}

impl std::fmt::Display for MyStruct {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "(value a: {}, value b: {})", self.a, self.b)
    }
}

fn main() {
    let test = MyStruct { a: 0, b: 0 };

    println!("Used Display: {}", test);    
}

Shell:

Used Display: (value a: 0, value b: 0)

For more information, you can look at the fmt module documentation.

You want to implement the Debug trait on your struct. Using #[derive(Debug)] is the easiest solution. Then you can print it with {:?}:

#[derive(Debug)]
struct MyStruct{
    a: i32,
    b: i32
}

fn main() {
    let x = MyStruct{ a: 10, b: 20 };
    println!("{:?}", x);
}