Loops in Rust (loop, while, for)

Analogy categoryAnalogies

Introduction

Rust provides three looping constructs: loop for an intentionally infinite loop, while for condition-based repetition, and for for iterating over a collection or range. Choosing the right one communicates intent clearly to readers of the code. A unique feature of loop is that it can return a value from the loop itself using break value;, which the other loop forms cannot do.

🏏

Cricket analogy: Rust's loop is like a bowler running unlimited trial deliveries until the coach calls break with a verdict value (the perfect line), while while repeats only as long as a fitness-test condition holds, and for strides through a fixed over count — each communicates intent clearly to teammates reading the drill plan.

Syntax

rust

// infinite loop, can return a value
let result = loop {
    // ...
    break some_value;
};

// condition-based loop
while condition {
    // ...
}

// iterator-based loop (idiomatic)
for item in iterable {
    // ...
}

// labeled loops for nested control
'outer: loop {
    loop {
        break 'outer;
    }
}

Explanation

loop repeats a block forever until an explicit break, and break can carry a value out of the loop, making loop useful for retry logic or computations where the exit condition is discovered mid-iteration. while repeats as long as a bool condition holds, checked before each iteration. for is the idiomatic choice for iterating over ranges (like 0..5) or any type implementing IntoIterator, such as vectors and arrays — it avoids manual index bookkeeping and out-of-bounds errors. Labeled loops, written as 'label: loop { ... }, let you break or continue a specific outer loop from within nested loops using break 'label; or continue 'label;.

🏏

Cricket analogy: loop suits DRS retries, where break carries out the final decision value once discovered mid-review; while re-checks "run rate achievable" before every over; for is the idiomatic way to iterate 0..overs or a batting lineup without manual index tracking; and a labeled 'powerplay: loop lets you break 'powerplay from a nested fielding-position loop.

Example

rust

fn main() {
    // loop returning a value
    let mut counter = 0;
    let doubled = loop {
        counter += 1;
        if counter == 5 {
            break counter * 2;
        }
    };
    println!("doubled = {}", doubled);

    // while loop
    let mut n = 3;
    while n != 0 {
        println!("n = {}", n);
        n -= 1;
    }

    // for loop over a range
    for i in 0..3 {
        println!("i = {}", i);
    }

    // labeled loops
    'outer: for x in 0..3 {
        for y in 0..3 {
            if x == 1 && y == 1 {
                break 'outer;
            }
            println!("x={}, y={}", x, y);
        }
    }
}

Output

text

doubled = 10
n = 3
n = 2
n = 1
i = 0
i = 1
i = 2
x=0, y=0
x=0, y=1
x=0, y=2
x=1, y=0

Key Takeaways

loop repeats indefinitely until break, and can return a value via break value;.
while repeats based on a bool condition checked before every iteration.
for is the idiomatic way to iterate ranges and collections via IntoIterator.
Labeled loops ('label:) let break and continue target a specific outer loop.
Choosing loop vs while vs for communicates intent and often prevents index errors.

Practice what you learned

1. Which loop construct in Rust can directly return a value using break?

2. What is the idiomatic way to iterate over a vector's elements in Rust?

3. What does the label in `'outer: loop { ... break 'outer; }` do?

4. When is the condition of a while loop evaluated?

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Topics covered

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Introduction

Syntax

Explanation

Example

Output

Key Takeaways

Practice what you learned

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