# Vectors

Vectors are re-sizable arrays. Like slices, their size is not known at compile time, but they can grow or shrink at any time. A vector is represented using 3 parameters:

• pointer to the data
• length
• capacity

The capacity indicates how much memory is reserved for the vector. The vector can grow as long as the length is smaller than the capacity. When this threshold needs to be surpassed, the vector is reallocated with a larger capacity.

``````fn main() {
// Iterators can be collected into vectors
let collected_iterator: Vec<i32> = (0..10).collect();
println!("Collected (0..10) into: {:?}", collected_iterator);

// The `vec!` macro can be used to initialize a vector
let mut xs = vec![1i32, 2, 3];
println!("Initial vector: {:?}", xs);

// Insert new element at the end of the vector
println!("Push 4 into the vector");
xs.push(4);
println!("Vector: {:?}", xs);

// Error! Immutable vectors can't grow
collected_iterator.push(0);
// FIXME ^ Comment out this line

// The `len` method yields the number of elements currently stored in a vector
println!("Vector length: {}", xs.len());

// Indexing is done using the square brackets (indexing starts at 0)
println!("Second element: {}", xs[1]);

// `pop` removes the last element from the vector and returns it
println!("Pop last element: {:?}", xs.pop());

// Out of bounds indexing yields a panic
println!("Fourth element: {}", xs[3]);
// FIXME ^ Comment out this line

// `Vector`s can be easily iterated over
println!("Contents of xs:");
for x in xs.iter() {
println!("> {}", x);
}

// A `Vector` can also be iterated over while the iteration
// count is enumerated in a separate variable (`i`)
for (i, x) in xs.iter().enumerate() {
println!("In position {} we have value {}", i, x);
}

// Thanks to `iter_mut`, mutable `Vector`s can also be iterated
// over in a way that allows modifying each value
for x in xs.iter_mut() {
*x *= 3;
}
println!("Updated vector: {:?}", xs);
}
``````

More `Vec` methods can be found under the std::vec module