56 lines
2.0 KiB
Markdown
56 lines
2.0 KiB
Markdown
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---
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title: Loops
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---
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# Loops
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Within Rust there are three kinds of native looping mechanisms: `loop`, `while`, and `for`.
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## Infinite repetition with `loop`
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In Rust, the `loop` structure will continually execute a block of code ad infinitum, (or until you explicitly tell it to stop).
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Here is an example program using `loop` to print the word 'again' continually to the terminal:
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```rust
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fn main() {
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loop {
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println!("again!");
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}
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}
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```
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## Conditional looping with `while`
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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.
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Here is an example program using `while` to count down from 5:
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```rust
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fn main() {
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let mut number = 5;
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while number != 0 {
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println!("{}", number);
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number = number - 1;
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}
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}
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```
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Run the code [here](https://play.rust-lang.org/?gist=62677371a8590be27c84dcae7068de57&version=stable).
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## Iterating through a collection with `for`
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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.
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Here is an example program that prints each number in an array to the terminal using `for`:
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```rust
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fn main() {
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let collection = [15, 7, 2, 6, 9];
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for element in collection.iter() {
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println!("the value is: {}", element);
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}
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}
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```
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Run the code [here](https://play.rust-lang.org/?gist=0c2acf21b96a81ebd411e4a7dc5a19fd&version=stable).
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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](https://doc.rust-lang.org/book/second-edition/ch03-05-control-flow.html).
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