While loop in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of this Rust program?

Rust

fn main() {
    let mut count = 0;
    while count < 3 {
        println!("{}", count);
        count += 1;
    }
}

A 0\n1\n2

B 1\n2\n3

C 0\n1\n2\n3

D 1\n2

💡 Hint

Remember the loop runs while count is less than 3, starting from 0.

The loop starts with count = 0 and prints it. It increments count by 1 each time. It stops before count reaches 3, so it prints 0, 1, and 2.

❓ Predict Output

intermediate

While loop with break condition

What will this Rust program print?

Rust

fn main() {
    let mut n = 5;
    while n > 0 {
        if n == 3 {
            break;
        }
        println!("{}", n);
        n -= 1;
    }
}

A 5\n4\n3

B 4\n3\n2\n1

C 5\n4

D 5\n4\n2\n1

💡 Hint

The loop stops when n equals 3 before printing it.

The loop prints n while n is greater than 0. When n reaches 3, the break stops the loop before printing 3. So it prints 5 and 4 only.

🔧 Debug

advanced

Identify the error in this while loop

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 RuntimeError: infinite loop

B SyntaxError: expected `;` after expression

C TypeError: mismatched types

D No error, prints 0 to 4

💡 Hint

Check the line endings inside the loop.

Rust requires semicolons at the end of statements. The line `i = i + 1` is missing a semicolon, causing a syntax error.

❓ Predict Output

advanced

While loop with nested if and continue

What is the output of this Rust program?

Rust

fn main() {
    let mut x = 0;
    while x < 5 {
        x += 1;
        if x % 2 == 0 {
            continue;
        }
        println!("{}", x);
    }
}

A 0\n1\n3\n5

B 2\n4

C 1\n2\n3\n4\n5

D 1\n3\n5

💡 Hint

The continue skips printing even numbers.

The loop increments x first. If x is even, it skips printing. So only odd numbers 1, 3, and 5 are printed.

🧠 Conceptual

expert

While loop behavior with mutable references

Consider this Rust code snippet. What will be the value of `counter` after the loop finishes?

Rust

fn main() {
    let mut counter = 0;
    let mut reference = &mut counter;
    while *reference < 4 {
        *reference += 1;
    }
    println!("{}", counter);
}

A 4

B 0

C 5

D Compilation error due to mutable borrow

💡 Hint

The mutable reference changes the original variable inside the loop.

The mutable reference `reference` points to `counter`. The loop increments the value through the reference until it reaches 4. So `counter` becomes 4.