Vectors

A ‘vector’ is a dynamic or ‘growable’ array, implemented as the standard library type `Vec<T>`. The `T` means that we can have vectors of any type (see the chapter on generics for more). Vectors always allocate their data on the heap. You can create them with the `vec!` macro:

fn main() { let v = vec![1, 2, 3, 4, 5]; // v: Vec<i32> }
```let v = vec![1, 2, 3, 4, 5]; // v: Vec<i32>
```

(Notice that unlike the `println!` macro we’ve used in the past, we use square brackets `[]` with `vec!` macro. Rust allows you to use either in either situation, this is just convention.)

There’s an alternate form of `vec!` for repeating an initial value:

fn main() { let v = vec![0; 10]; // ten zeroes }
```let v = vec![0; 10]; // ten zeroes
```

Accessing elements

To get the value at a particular index in the vector, we use `[]`s:

fn main() { let v = vec![1, 2, 3, 4, 5]; println!("The third element of v is {}", v[2]); }
```let v = vec![1, 2, 3, 4, 5];

println!("The third element of v is {}", v[2]);
```

The indices count from `0`, so the third element is `v[2]`.

Iterating

Once you have a vector, you can iterate through its elements with `for`. There are three versions:

fn main() { let mut v = vec![1, 2, 3, 4, 5]; for i in &v { println!("A reference to {}", i); } for i in &mut v { println!("A mutable reference to {}", i); } for i in v { println!("Take ownership of the vector and its element {}", i); } }
```let mut v = vec![1, 2, 3, 4, 5];

for i in &v {
println!("A reference to {}", i);
}

for i in &mut v {
println!("A mutable reference to {}", i);
}

for i in v {
println!("Take ownership of the vector and its element {}", i);
}
```

Vectors have many more useful methods, which you can read about in their API documentation.