Loop execution flow in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested loops with break

What is the output of this Rust code snippet?

Rust

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

A 9

B 5

C 7

D 6

💡 Hint

Count how many times the inner loop runs before break triggers.

The inner loop breaks when i*j > 4. Counting iterations: i=1 (j=1,2,3) all <=4, count=3; i=2 (j=1,2) 2*3=6>4 break at j=3, count=5; i=3 (j=1) 3*2=6>4 break at j=2, count=6 total.

❓ Predict Output

intermediate

Loop with continue and variable update

What will be printed by this Rust program?

Rust

fn main() {
    let mut sum = 0;
    for x in 1..=5 {
        if x % 2 == 0 {
            continue;
        }
        sum += x;
    }
    println!("{}", sum);
}

A 6

B 9

C 15

D 10

💡 Hint

Sum only odd numbers from 1 to 5.

The loop skips even numbers (2,4). Sum is 1 + 3 + 5 = 9.

🔧 Debug

advanced

Identify the error in this loop

What error will this Rust code produce when compiled?

Rust

fn main() {
    let mut i = 0;
    loop {
        if i == 5 {
            break;
        }
        i += 1;
    }
    println!("{}", i);
}

A No error, prints 5

B RuntimeError: infinite loop

C SyntaxError: missing semicolon after i += 1

D SyntaxError: missing curly brace

💡 Hint

Check if all statements end properly.

The original code was missing a semicolon after 'i += 1'. Adding the semicolon fixes the syntax error, so the code compiles and prints 5.

❓ Predict Output

advanced

Loop with labeled break

What will this Rust program print?

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 2

B 6

C 9

D 3

💡 Hint

The labeled break exits both loops when i+j == 4.

The labeled break exits the outer loop when i+j == 4. For i=1: j=1 (2!=4) count=1; j=2 (3!=4) count=2; j=3 (4==4) break 'outer (no increment). No further iterations. Total count=2.

❓ Predict Output

expert

Complex loop with multiple control flow statements

What is the final value of `result` after running this Rust code?

Rust

fn main() {
    let mut result = 0;
    let mut i = 0;
    while i < 5 {
        i += 1;
        if i == 3 {
            continue;
        }
        if i == 4 {
            break;
        }
        result += i;
    }
    println!("{}", result);
}

A 6

B 5

C 3

D 4

💡 Hint

Trace each iteration and note when continue and break happen.

i=1 result=1; i=2 result=3; i=3 continue (skip adding); i=4 break loop; final result=3.