loop / while / for

// Infinite loop. You can return a value with break.
let result = loop {
    // ...
    break 42;  // 42 is assigned to result.
};

// Loops while the condition is true.
while condition {
    // ...
}

// Iterates over an iterator (most commonly used).
for x in 0..5 {          // 0, 1, 2, 3, 4
    // ...
}
for x in 0..=5 {         // 0, 1, 2, 3, 4, 5 (inclusive end)
    // ...
}
for item in &vec {        // Borrows each element of the slice.
    // ...
}

// Control loop execution.
break;     // Exits the loop.
continue;  // Skips to the next iteration.

fn main() {
    // loop: infinite loop that returns a value via break.
    let mut count = 0;
    let result = loop {
        count += 1;
        if count == 5 {
            break count * 2;  // The break value is assigned to result.
        }
    };
    println!("loop result: {}", result);  // 10

    // while: conditional loop example.
    let mut n = 1;
    while n < 32 {
        print!("{} ", n);
        n *= 2;
    }
    println!();  // 1 2 4 8 16

    // while let: loops while the Option is Some.
    let mut stack = vec![1, 2, 3];
    while let Some(top) = stack.pop() {
        print!("{} ", top);  // 3 2 1
    }
    println!();

    // for + range: 0..5 covers 0 through 4.
    print!("0..5: ");
    for i in 0..5 {
        print!("{} ", i);
    }
    println!();

    // for + inclusive range: 0..=5 covers 0 through 5.
    print!("0..=5: ");
    for i in 0..=5 {
        print!("{} ", i);
    }
    println!();

    // for + borrowed slice.
    let fruits = ["apple", "banana", "cherry"];
    for fruit in &fruits {
        println!("fruit: {}", fruit);
    }

    // Use enumerate to get both the index and the value.
    for (i, fruit) in fruits.iter().enumerate() {
        println!("  [{}] {}", i, fruit);
    }

    // Use a labeled loop to break out of nested loops.
    'outer: for x in 0..3 {
        for y in 0..3 {
            if x == 1 && y == 1 {
                println!("Breaking outer loop at ({},{})", x, y);
                break 'outer;
            }
            print!("({},{}) ", x, y);
        }
    }
    println!();
}

In Rust, the for loop works closely with the iterator protocol. When iterating over a slice or array by reference, make sure to use & — omitting it moves ownership into the loop.

loop is equivalent to while true in other languages, but with the ability to return a value. When you need to exit a loop based on a condition variable, loop with break is often more idiomatic Rust than while.

Rust has no C-style for(int i=0; i<n; i++). Use for i in 0..n instead.

For conditional branching, see 'if / else / if let'. For pattern matching, see 'match / Pattern Matching'.