Loop execution flow in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic purpose of a loop in Rust?

A loop repeats a block of code multiple times until a condition is met or the loop is explicitly stopped.

beginner

What keyword is used in Rust to create an infinite loop?

The keyword loop creates an infinite loop that runs until it is stopped with break.

beginner

How does the break statement affect loop execution?

The break statement immediately stops the loop and exits it, continuing with the code after the loop.

intermediate

What does the continue statement do inside a loop?

The continue statement skips the rest of the current loop cycle and moves to the next iteration.

intermediate

How can you label loops in Rust and why would you do that?

You can add a label like 'label: before a loop to identify it. This helps control nested loops by specifying which loop to break or continue.

Which Rust keyword creates a loop that runs forever unless stopped?

A loop

B while

C for

D repeat

The loop keyword creates an infinite loop in Rust.

What happens when break is executed inside a loop?

A The program crashes

B The loop skips to the next iteration

C The loop restarts from the beginning

D The loop stops immediately

break stops the loop immediately and continues after the loop.

What does continue do inside a loop?

A Skips the rest of the current iteration

B Stops the loop

C Exits the program

D Restarts the entire loop

continue skips the rest of the current loop cycle and moves to the next iteration.

How do you label a loop in Rust?

A label loop { ... }

B 'label: loop { ... }

C loop 'label { ... }

D loop label: { ... }

You add a label before the loop like 'label: loop { ... }.

Why use loop labels in Rust?

A To name variables inside the loop

B To create infinite loops

C To control which nested loop to break or continue

D To speed up the loop

Labels help specify which nested loop to control with break or continue.

Explain how break and continue affect the flow of a loop in Rust.

Think about what happens when you want to stop or skip inside a loop.

Describe how loop labels work and give an example of when you might need them.

Consider nested loops and controlling them precisely.

Practice

1. What does the break statement do inside a Rust loop?

easy

A. It restarts the loop from the beginning.

B. It skips the current iteration and continues with the next one.

C. It pauses the loop until a condition is met.

D. It stops the loop immediately and exits it.

Solution

1. Step 1: Understand the role of break in loops

   The break statement immediately stops the loop and exits it.

2. Step 2: Compare with other loop controls

   continue skips to the next iteration, but break ends the loop entirely.

3. Final Answer:

   It stops the loop immediately and exits it. -> Option D

4. Quick Check:

   break stops loop = C [OK]

Hint: Remember: break = stop loop, continue = skip iteration [OK]

Common Mistakes:

• Confusing break with continue
• Thinking break pauses instead of stops
• Assuming break restarts the loop

2. Which of the following is the correct syntax to skip the current iteration in a Rust for loop?

easy

A. skip;

B. continue;

C. break;

D. next;

Solution

1. Step 1: Identify the keyword to skip iteration

   In Rust, continue; skips the rest of the current loop iteration and moves to the next.

2. Step 2: Check other options for correctness

   break; stops the loop, skip; and next; are not valid Rust keywords for this purpose.

3. Final Answer:

   continue; -> Option B

4. Quick Check:

   Skip iteration = continue [OK]

Hint: Use continue to skip current loop iteration [OK]

Common Mistakes:

• Using break instead of continue
• Using non-existent keywords like skip or next
• Omitting the semicolon

3. What will be the output of this Rust code?

let mut count = 0;
loop {
    count += 1;
    if count == 3 {
        break;
    }
    println!("{}", count);
}

medium

A. 1 2 3

B. 0 1 2

C. 1 2

D. 3

Solution

1. Step 1: Trace the loop iterations and print statements

   Loop increments count from 0 to 1, prints 1; then 2, prints 2; when count is 3, break stops loop before printing.

2. Step 2: Determine printed values

   Only 1 and 2 are printed before break stops the loop.

3. Final Answer:

   1 2 -> Option C

4. Quick Check:

   Prints before break = 1 2 [OK]

Hint: Break stops before printing count 3 [OK]

Common Mistakes:

• Assuming count 3 is printed
• Starting count from 1 instead of 0
• Confusing break and continue effects

4. Identify the error in this Rust loop code:

for i in 1..5 {
    if i == 3 {
        continue
    }
    println!("{}", i);
}

medium

A. Missing semicolon after continue

B. Incorrect range syntax

C. println! macro is used incorrectly

D. continue cannot be used inside for loops

Solution

1. Step 1: Check syntax of continue statement

   In Rust, statements like continue require a semicolon to end the statement.

2. Step 2: Verify other parts of the code

   The range 1..5 and println! usage are correct; continue is valid inside for loops.

3. Final Answer:

   Missing semicolon after continue -> Option A

4. Quick Check:

   Statements need semicolon = A [OK]

Hint: Add semicolon after continue to fix syntax [OK]

Common Mistakes:

• Forgetting semicolon after continue
• Thinking continue is invalid in for loops
• Misreading range syntax

5. Given this Rust code, what will be the final value of sum?

let mut sum = 0;
for i in 1..6 {
    if i % 2 == 0 {
        continue;
    }
    if i == 5 {
        break;
    }
    sum += i;
}

hard

A. 4

B. 5

C. 6

D. 9

Solution

1. Step 1: Analyze loop iterations and conditions

   Loop runs i from 1 to 5 (exclusive 6). For even i, continue skips adding. For i == 5, break stops loop before adding.

2. Step 2: Calculate sum for valid i values

   i=1 (odd, add 1), i=2 (even, skip), i=3 (odd, add 3), i=4 (even, skip), i=5 (break before add). sum = 1 + 3 = 4.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Sum odd before 5 = 4 [OK]

Hint: Add only odd numbers before 5, skip evens [OK]

Common Mistakes:

• Adding even numbers mistakenly
• Including 5 in sum despite break
• Confusing continue and break effects