Learn Rust Coding · Lesson

Indexing and Iterating

Access and loop over elements.

Reading by Index

Each element in a vector has a position number called an index. Indexes start at 0, so the first element is index 0.

Read an element with square brackets, like v[0] for the first value.

fn main() {
    let v = vec![100, 200, 300];
    println!("first = {}", v[0]);
    println!("third = {}", v[2]);
}

Indexing past the end of a vector causes a panic and stops the program. For a vector of length 3, the only valid indexes are 0, 1, and 2.

Asking for v[5] here would crash, so always make sure the index is in range.