While loop in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a while loop that counts down from 3 to 1.

Rust

let mut count = 3;
while [1] {
    println!("{}", count);
    count -= 1;
}

Drag options to blanks, or click blank then click option'

Acount >= 5

Bcount < 0

Ccount == 0

Dcount > 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a condition that never becomes false, causing an infinite loop.

Using count == 0 which stops the loop immediately.

The condition count > 0 keeps the loop running while count is positive, counting down from 3 to 1.

2fill in blank

medium

Complete the code to print numbers from 1 to 5 using a while loop.

Rust

let mut num = 1;
while [1] {
    println!("{}", num);
    num += 1;
}

Drag options to blanks, or click blank then click option'

Anum <= 5

Bnum > 5

Cnum < 5

Dnum == 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using num < 5 which stops before printing 5.

Using num == 5 which runs only once.

The condition num <= 5 ensures the loop prints numbers 1 through 5 inclusive.

3fill in blank

hard

Fix the error in the while loop condition to avoid an infinite loop.

Rust

let mut x = 0;
while [1] {
    println!("{}", x);
    x += 1;
    if x == 3 {
        break;
    }
}

Drag options to blanks, or click blank then click option'

Ax < 3

Bx > 3

Ctrue

Dx == 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a condition that never becomes false without a break causes infinite loop.

Using x < 3 would also work but the task asks to fix the error with break.

Using true creates an infinite loop, but the break statement stops it when x == 3.

4fill in blank

hard

Fill both blanks to create a while loop that prints even numbers less than 10.

Rust

let mut n = 0;
while [1] {
    println!("{}", n);
    n [2] 2;
}

Drag options to blanks, or click blank then click option'

An < 10

Bn <= 10

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= 10 includes 10 which is not less than 10.

Using -= 2 decreases n causing an infinite loop.

The loop runs while n < 10 and increments n by 2 each time to print even numbers.

5fill in blank

hard

Fill all three blanks to create a while loop that collects numbers less than 5 into a vector.

Rust

let mut v = Vec::new();
let mut i = 0;
while [1] {
    v.push([2]);
    i [3] 1;
}

Drag options to blanks, or click blank then click option'

Ai < 5

Bi

C+=

Dv.len() < 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using v.len() < 5 in the condition can cause confusion.

Forgetting to increment i causes an infinite loop.

The loop runs while i < 5, pushes i into the vector, and increments i by 1 each time.

Practice

1.

What does a while loop do in Rust?

easy

A. Stops the program immediately

B. Runs code only once

C. Repeats code a fixed number of times

D. Repeats code as long as a condition is true

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly while its condition is true.

2. Step 2: Compare options with this behavior

   Only Repeats code as long as a condition is true describes repeating code while a condition is true.

3. Final Answer:

   Repeats code as long as a condition is true -> Option D

4. Quick Check:

   while loop = repeat while true [OK]

Hint: While loops run while condition is true [OK]

Common Mistakes:

• Confusing while loop with for loop
• Thinking while loop runs fixed times
• Believing while loop runs once only

2.

Which of the following is the correct syntax for a while loop in Rust?

??? x < 5 {
    println!("{}", x);
    x += 1;
}

easy

A. while

B. loop

C. for

D. if

Solution

1. Step 1: Identify the keyword for a while loop

   The keyword to start a while loop is while.

2. Step 2: Check other keywords

   loop is an infinite loop, for is for fixed iteration, if is conditional, not looping.

3. Final Answer:

   while -> Option A

4. Quick Check:

   while keyword starts while loop [OK]

Hint: While loops start with 'while' keyword [OK]

Common Mistakes:

• Using 'loop' instead of 'while'
• Using 'for' for while loops
• Using 'if' instead of loop keyword

3.

What will be the output of this Rust code?

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

medium

A. No output

B. 1 2 3 4

C. 1 2 3

D. 0 1 2

Solution

1. Step 1: Analyze the loop condition and variable

   The loop runs while count is less than or equal to 3, starting at 1.

2. Step 2: Trace the output values

   It prints 1, then 2, then 3, then stops because count becomes 4.

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Prints 1 to 3 inclusive [OK]

Hint: Count from 1 to 3 prints 1 2 3 [OK]

Common Mistakes:

• Thinking it prints 4
• Starting count at 0
• Assuming no output

4.

Find the error in this Rust code using a while loop:

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

medium

A. Wrong comparison operator in while condition

B. Missing increment of 'i' inside the loop

C. 'i' should be immutable, not mutable

D. println! macro syntax is incorrect

Solution

1. Step 1: Check loop variable update

   The variable 'i' is never increased inside the loop, so the condition never becomes false.

2. Step 2: Understand effect of missing increment

   Without increment, the loop runs forever (infinite loop).

3. Final Answer:

   Missing increment of 'i' inside the loop -> Option B

4. Quick Check:

   Increment needed to avoid infinite loop [OK]

Hint: Always update loop variable inside while loop [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Using wrong operator but code still compiles
• Misunderstanding mutability requirement

5.

Write a while loop in Rust that prints all even numbers from 2 to 10 inclusive.

Which code snippet correctly does this?

???

hard

A. let mut n = 2;
while n <= 10 {
println!("{}", n);
n += 2;
}

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

C. let mut n = 2;
while n < 10 {
println!("{}", n);
n += 2;
}

D. let mut n = 0;
while n <= 10 {
println!("{}", n);
n += 2;
}

Solution

1. Step 1: Check the range and values printed

   We want even numbers from 2 to 10 inclusive, so start at 2 and go up to 10.

2. Step 2: Analyze each option

   let mut n = 2; while n <= 10 { println!("{}", n); n += 2; } starts at 2, increments by 2, and stops at 10 inclusive. let mut n = 1; while n < 10 { if n % 2 == 0 { println!("{}", n); } n += 1; } starts at 1 and checks evenness each time but stops before 10, missing 10. let mut n = 2; while n < 10 { println!("{}", n); n += 2; } stops before 10, missing 10. let mut n = 0; while n <= 10 { println!("{}", n); n += 2; } starts at 0, which is even but outside the requested range.

3. Final Answer:

   let mut n = 2; while n <= 10 { println!("{}", n); n += 2; } -> Option A

4. Quick Check:

   Start 2, step 2, end 10 inclusive [OK]

Hint: Start at 2, add 2 each loop until 10 [OK]

Common Mistakes:

• Starting at 0 instead of 2
• Stopping before 10
• Not incrementing by 2