freeCodeCamp/guide/english/rust/loops/index.md

title
Loops

Loops

Within Rust there are three kinds of native looping mechanisms: loop, while, and for.

Infinite repetition with loop

In Rust, the loop structure will continually execute a block of code ad infinitum, (or until you explicitly tell it to stop).

Here is an example program using loop to print the word 'again' continually to the terminal:

fn main() {
    loop {
        println!("again!");
    }
}

Conditional looping with while

The above mechanism is not very useful unless we introduce some kind of stopping condition for the loop to check for. Luckily, Rust has an in-built looping structure called while, that you can use to continually execute a block of code whilst some condition is true.

Here is an example program using while to count down from 5:

fn main() {
    let mut number = 5;

    while number != 0 {
        println!("{}", number);
        number = number - 1;
    }
}

Run the code here.

Iterating through a collection with for

In some instances, you might want to iterate and operate on the elements of a collection (such as an array). Whilst you could achieve this using a while loop and an index variable to access each element, Rust provides the for loop to make this operation much easier.

Here is an example program that prints each number in an array to the terminal using for:

fn main() {
    let collection = [15, 7, 2, 6, 9];

    for element in collection.iter() {
        println!("the value is: {}", element);
    }
}

Run the code here.

Much like iterators in C++, the .iter() function returns an iterator to the collection, which can then be looped through to access each element. For more information, head to the Rust documentation on control flow.