What is a Vector?

Part of the Logic & Flow section of Coddy's Rust journey — lesson 7 of 66.

In Rust, you have two main ways to store collections of data: arrays and vectors. While arrays have a fixed size that must be known at compile time, vectors are dynamic collections that can grow and shrink during program execution.

A vector, written as Vec<T>, is Rust's growable array type. The T represents the type of elements the vector will hold - for example, Vec<i32> for integers or Vec<String> for strings. Unlike arrays where you must specify the exact number of elements upfront, vectors can start empty and have elements added or removed as your program runs.

Here's when you'd choose a vector over an array:

// Array - fixed size, known at compile time
let scores = [85, 92, 78, 90]; // always exactly 4 elements

// Vector - dynamic size, can change during runtime
let mut grades = Vec::new(); // starts empty, can grow

Vectors are perfect when you don't know how many items you'll need in advance, such as storing user input, reading data from files, or building lists that change based on program logic. They provide the flexibility that arrays cannot offer while maintaining efficient access to elements.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Cheat sheet

Vectors (Vec<T>) are dynamic collections that can grow and shrink during program execution, unlike arrays which have a fixed size known at compile time.

The T represents the type of elements the vector will hold:

Vec<i32>    // vector of integers
Vec<String> // vector of strings

Creating a vector:

let mut grades = Vec::new(); // starts empty, can grow

Comparison with arrays:

// Array - fixed size
let scores = [85, 92, 78, 90]; // always exactly 4 elements

// Vector - dynamic size
let mut grades = Vec::new(); // can change during runtime

Use vectors when you don't know how many items you'll need in advance, such as storing user input, reading data from files, or building lists that change based on program logic.

Try it yourself

This lesson doesn't include a code challenge.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.