Loop construct in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a nested loop with break

What is the output of this Rust code snippet?

Rust

fn main() {
    let mut count = 0;
    'outer: for i in 1..=3 {
        for j in 1..=3 {
            if i * j > 4 {
                break 'outer;
            }
            count += 1;
        }
    }
    println!("{}", count);
}

A 6

B 9

C 5

D 4

💡 Hint

Remember that break with label exits the outer loop immediately.

The inner loop increments count while i*j <= 4. When i=2 and j=3, i*j=6 > 4, so break 'outer stops all loops. The count increments 5 times before breaking.

🧠 Conceptual

intermediate

Understanding loop labels in Rust

Which statement best describes the purpose of loop labels in Rust?

A They automatically count the number of iterations.

B They are used to name variables inside loops.

C They define the type of loop (for, while, or loop).

D They allow breaking or continuing an outer loop from inside an inner loop.

💡 Hint

Think about how to control nested loops.

Loop labels let you specify which loop to break or continue when loops are nested, avoiding ambiguity.

❓ Predict Output

advanced

Output of a loop with match and continue

What is the output of this Rust program?

Rust

fn main() {
    let mut x = 0;
    let mut result = 0;
    loop {
        x += 1;
        match x {
            3 => continue,
            5 => break,
            _ => result += x,
        }
    }
    println!("{}", result);
}

A 7

B 9

C 10

D 15

💡 Hint

Remember that continue skips the rest of the loop body for that iteration.

The loop adds x to result except when x is 3 (skips adding) and stops when x is 5. So result = 1+2+4 = 7 + 5 skipped + break at 5.

🔧 Debug

advanced

Identify the error in this loop code

What error will this Rust code produce when compiled?

Rust

fn main() {
    let mut i = 0;
    while i < 5 {
        println!("{}", i);
        i = i + 1;
    }
}

A SyntaxError: missing semicolon after i = i + 1

B RuntimeError: infinite loop

C TypeError: cannot add integer to mutable variable

D No error, prints numbers 0 to 4

💡 Hint

Check punctuation carefully in Rust statements.

Rust requires semicolons at the end of statements. Missing semicolon after i = i + 1 causes a syntax error.

🚀 Application

expert

Calculate sum of even numbers using loop and continue

Which Rust code correctly calculates the sum of even numbers from 1 to 10 using a loop and continue?

A

let mut sum = 0;
for n in 1..=10 {
    if n % 2 == 0 { continue; }
    sum += n;
}
println!("{}", sum);

B

let mut sum = 0;
let mut n = 1;
loop {
    if n > 10 { break; }
    if n % 2 != 0 { n += 1; continue; }
    sum += n;
    n += 1;
}
println!("{}", sum);

C

let mut sum = 0;
let mut n = 1;
while n <= 10 {
    if n % 2 == 0 { sum += n; }
    n += 1;
}
println!("{}", sum);

D

let mut sum = 0;
let mut n = 1;
loop {
    if n > 10 { break; }
    if n % 2 == 0 { sum += n; }
    n += 1;
}
println!("{}", sum);

💡 Hint

Use continue to skip odd numbers inside the loop.

Option B uses loop and continue correctly to skip odd numbers and sum even numbers. Option B incorrectly continues on even numbers. Option B uses while but no continue. Option B sums even numbers but does not use continue.