Loop execution flow in Rust - Mini Project: Build & Apply

Loop Execution Flow in Rust

📖 Scenario: You are helping a small bakery keep track of how many cakes they bake each day. They want to count cakes baked in a simple loop.

🎯 Goal: Build a Rust program that uses a loop to count cakes baked from 1 to 5 and then stops.

📋 What You'll Learn

Create a variable to count cakes baked

Use a loop to increase the count

Stop the loop when 5 cakes are counted

Print the final count

💡 Why This Matters

🌍 Real World

Counting repeated actions like baked cakes helps bakeries track production easily.

💼 Career

Understanding loop flow is key for programming tasks that repeat steps until a condition is met.

1

Create a cake counter variable

Create a variable called cakes_baked and set it to 0.

Rust

# Create a variable called cakes_baked and set it to 0
# Your code here

Hint

Use let mut to create a variable you can change later.

2

Set up a loop to count cakes

Add a loop block inside main that will run repeatedly.

Rust

fn main() {
    let mut cakes_baked = 0;
    // Add a loop here
    // Your code here
}

Hint

Use loop { } to create an infinite loop that you will control inside.

3

Increase the cake count and stop at 5

Inside the loop, add code to increase cakes_baked by 1 each time. Then use if cakes_baked == 5 to break the loop.

Rust

fn main() {
    let mut cakes_baked = 0;
    loop {
        // Increase cakes_baked by 1
        // Stop loop if cakes_baked is 5
        // Your code here
    }
}

Hint

Use += 1 to add one to the count. Use break to stop the loop.

4

Print the final cake count

After the loop, write println!("Cakes baked: {}", cakes_baked); to show the total cakes baked.

Rust

fn main() {
    let mut cakes_baked = 0;
    loop {
        cakes_baked += 1;
        if cakes_baked == 5 {
            break;
        }
    }
    // Print the total cakes baked
    // Your code here
}

Hint

Use println! to show the result on the screen.

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