Match guards in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of match with guard on integer

What is the output of this Rust code snippet?

Rust

fn main() {
    let x = 7;
    match x {
        n if n % 2 == 0 => println!("Even"),
        n if n % 2 == 1 => println!("Odd"),
        _ => println!("Unknown"),
    }
}

A Odd

B Even

C Unknown

D Compilation error

💡 Hint

Check the value of x and the conditions in the match guards.

The value 7 is odd, so the guard n % 2 == 1 matches and prints "Odd".

❓ Predict Output

intermediate

Match guard with multiple conditions

What will this Rust program print?

Rust

fn main() {
    let c = 'g';
    match c {
        ch if ch.is_ascii_lowercase() && ch < 'm' => println!("First half lowercase"),
        ch if ch.is_ascii_lowercase() => println!("Second half lowercase"),
        _ => println!("Not lowercase"),
    }
}

A First half lowercase

B Second half lowercase

C Not lowercase

D Runtime panic

💡 Hint

Check the character 'g' against the conditions in order.

'g' is lowercase and 'g' < 'm', so the first guard matches.

❓ Predict Output

advanced

Match guard with tuple and shadowing

What is the output of this Rust code?

Rust

fn main() {
    let pair = (3, -2);
    match pair {
        (x, y) if x == y => println!("Equal"),
        (x, y) if x + y == 0 => println!("Sum zero"),
        _ => println!("No match"),
    }
}

A Equal

B Compilation error

C No match

D Sum zero

💡 Hint

Check the values of x and y and the guards in order.

3 + (-2) == 1, so the second guard is false; the first guard x == y is false; so it prints "No match".

❓ Predict Output

advanced

Match guard with range and variable binding

What will this Rust program print?

Rust

fn main() {
    let num = 15;
    match num {
        n @ 1..=10 if n % 2 == 0 => println!("Even in 1 to 10"),
        n @ 11..=20 if n % 3 == 0 => println!("Multiple of 3 in 11 to 20"),
        _ => println!("Other"),
    }
}

A Even in 1 to 10

B Other

C Compilation error

D Multiple of 3 in 11 to 20

💡 Hint

Check which range 15 falls into and if it is divisible by 3.

15 is in 11..=20 and divisible by 3, so it prints "Multiple of 3 in 11 to 20".

❓ Predict Output

expert

Match guard with enum and complex condition

Given this Rust code, what is the output?

Rust

enum Status {
    Active(i32),
    Inactive(i32),
}

fn main() {
    let s = Status::Active(10);
    match s {
        Status::Active(n) if n > 5 && n < 15 => println!("Active and moderate"),
        Status::Active(n) if n >= 15 => println!("Active and high"),
        Status::Inactive(_) => println!("Inactive"),
        _ => println!("Unknown"),
    }
}

A Active and high

B Active and moderate

C Inactive

D Unknown

💡 Hint

Check the enum variant and the value inside it against the guards.

The value is Active(10), which satisfies n > 5 && n < 15, so it prints "Active and moderate".