For loop in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust for loop?

Consider the following Rust code. What will it print?

Rust

fn main() {
    let mut sum = 0;
    for i in 1..5 {
        sum += i;
    }
    println!("{}", sum);
}

A Error: cannot add i to sum

B 15

C 14

D 10

💡 Hint

Remember that 1..5 in Rust means 1 up to but not including 5.

The loop runs for i = 1, 2, 3, 4. Their sum is 1+2+3+4 = 10.

🧠 Conceptual

intermediate

How many times does this Rust for loop run?

How many iterations will this loop execute? for x in (0..10).step_by(3) { println!("{}", x); }

A 4

B Error: step_by requires usize

C 10

D 3

💡 Hint

Count numbers from 0 to 9 stepping by 3.

The loop runs for x = 0, 3, 6, 9, so 4 times.

❓ Predict Output

advanced

What is the output of this nested for loop?

Analyze the output of this Rust code snippet:

Rust

fn main() {
    for i in 1..3 {
        for j in 1..=i {
            print!("{}{} ", i, j);
        }
    }
}

A 11 21

B 11 12 21 22

C 11 21 22

D 12 22

💡 Hint

Remember that 1..3 means 1 and 2, and 1..=i includes i.

Outer loop i=1: inner j=1 prints '11 '. Outer loop i=2: inner j=1,2 prints '21 22 '.

🔧 Debug

advanced

What error does this Rust for loop code produce?

Identify the error when running this code:

Rust

fn main() {
    let mut numbers = vec![1, 2, 3];
    for num in numbers.iter() {
        numbers.push(*num + 1);
    }
}

A Compile error: cannot borrow `numbers` as mutable while iterating

B Syntax error: missing semicolon

C No error, prints numbers

D Compile error: cannot move out of `numbers`

💡 Hint

Think about modifying a vector while looping over it.

You cannot mutate a vector by pushing to it while iterating over it, causing a compile error.

🚀 Application

expert

What is the final value of `result` after this loop?

Given this Rust code, what is the value of `result` after the loop finishes?

Rust

fn main() {
    let mut result = 1;
    for i in (1..=4).rev() {
        if i % 2 == 0 {
            result *= i;
        }
    }
    println!("{}", result);
}

A 24

B 8

C 4

D 0

💡 Hint

Multiply only even numbers from 4 down to 1.

Even numbers in 4..=1 reversed are 4 and 2. Multiplying 1*4*2 = 8.