Loops in Rust

ByWalter Wimberly

Rust has the standard loops one might expect, such as a while (conditional) style loop, and a for (counting) loop. As with most modern languages, it also has a for each style loop.

A Bad Type of Loop…

One thing that is unique however, is that it also includes a built in infinite loop, which many (myself include) consider to be bad form. You can use the continue command to start the loop over, skipping any content after that line inside of the loop, as well as a break, to exit the loop.

let mut count = 0;

println!("Let's count until infinity!");

// how long will this go on for???
loop {
  count += 1;
  println!("{}", count);
  // I could put a break here... or there... or anywhere else if I want to make this difficult to debug.
}

Conditional Loops

A while loop is standard for Rust, and works like most languages, except there is no parenthesis for the condition, similar to how Rust handles conditional statements for their if statements.

This is an example of the famous fizzbuzz application.

fn main() {
    // A counter variable
    let mut n = 1;

    // Loop while `n` is less than 101
    while n < 101 {
        if n % 15 == 0 {
            println!("fizzbuzz");
        } else if n % 3 == 0 {
            println!("fizz");
        } else if n % 5 == 0 {
            println!("buzz");
        } else {
            println!("{}", n);
        }

        // Increment counter
        n += 1;
    }
}

For (Counting) Loops

A for loop in Rust is similar to what you might see in Ruby, or some other newer languages, where you have a starting and ending condition. However, while the initial condition is inclusive, the external is not:

fn main() {
    // `n` will take the values: 1, 2,up to 50
    for n in 1..51 {
        if n % 15 == 0 {
            println!("fizzbuzz");
        } else if n % 3 == 0 {
            println!("fizz");
        } else if n % 5 == 0 {
            println!("buzz");
        } else {
            println!("{}", n);
        }
    }
}

If you want to include the final number, use ..=.

fn main() {
    // `n` will take the values: 1, 2,up to 51
    for n in 1..=51 {
        if n % 15 == 0 {
            println!("fizzbuzz");
        } else if n % 3 == 0 {
            println!("fizz");
        } else if n % 5 == 0 {
            println!("buzz");
        } else {
            println!("{}", n);
        }
    }
}

For Each Style (Range)

Rust has a for ... in style command, similar to other languages for each, where you can iterate over a series of data that allows iteration.

fn main() {
    let names = ["Bruce", "Clark", "Diana"];

    for name in names.iter() {
        println!("Hello {}", name);
    }
    
    println!("names: {:?}", names);
}

Rust actually has several different types of iterators, but we’re just going to look at iter() for this instance.

Loops in Rust was originally found on Access 2 Learn

Assistant Professor

Walter Wimberly is an Assistant Professor at a regional college in Tennessee, teaching Computer Science in the Software Engineering track. He works as a student advisor, oversees curriculum changes, develops new courses, and manages the advisory panel.
Walter taught full time for about 7 years, before going back into “industry” as a full stack Software Developer for a dozen years. There he focused on web based projects coding in JavaScript/jQuery and utilizing the Bootstrap CSS Framework on the front-end, and coding in PHP, ASP/ASP.Net, SQL on the back-end.

Since he loves teaching, he taught as an adjunct web and digital media classes for eight (8) years, while working in industry, and has since returned to teaching full time.

He has been married for over 25 years, and is father to several special needs boys. As such, he is working on some projects to help others who have special needs to be self-sufficient, and support the care givers of those with special needs. Check out his Autism blog for more info.

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