Loop construct in Rust - Mini Project: Build & Apply

Loop construct in Rust

📖 Scenario: You are helping a small shop owner count the total number of items sold in a day. The shop owner has a list of daily sales numbers for each hour.

🎯 Goal: Build a Rust program that uses a loop construct to sum all the sales numbers and print the total.

📋 What You'll Learn

Create a vector called sales with the exact values: 5, 8, 12, 3, 7

Create a variable called total and set it to 0

Use a loop construct with an index variable i to iterate over sales

Add each sale to total inside the loop

Break the loop when all sales are added

Print the final total value

💡 Why This Matters

🌍 Real World

Counting totals from lists of numbers is common in sales, inventory, and data analysis.

💼 Career

Understanding loops and data structures like vectors is essential for software development and data processing jobs.

1

Create the sales data

Create a vector called sales with the exact values 5, 8, 12, 3, 7.

Rust

# Create a vector called sales with values 5, 8, 12, 3, 7
// Your code here

Hint

Use let sales = vec![5, 8, 12, 3, 7]; to create the vector.

2

Initialize the total counter

Create a variable called total and set it to 0 inside the main function, below the sales vector.

Rust

fn main() {
    let sales = vec![5, 8, 12, 3, 7];
    // Create a variable called total and set it to 0
    // Your code here
}

Hint

Use let mut total = 0; to create a variable that can change.

3

Use a loop to sum sales

Use a loop construct with an index variable i starting at 0 to iterate over the sales vector. Inside the loop, add sales[i] to total. Break the loop when i reaches the length of sales.

Rust

fn main() {
    let sales = vec![5, 8, 12, 3, 7];
    let mut total = 0;
    // Use a loop with index i to sum sales
    // Your code here
}

Hint

Start with let mut i = 0;. Use loop { ... }. Inside, check if i == sales.len() to break. Add sales[i] to total and increase i by 1.

4

Print the total sales

Add a println! statement to print the total variable after the loop ends.

Rust

fn main() {
    let sales = vec![5, 8, 12, 3, 7];
    let mut total = 0;
    let mut i = 0;
    loop {
        if i == sales.len() {
            break;
        }
        total += sales[i];
        i += 1;
    }
    // Print the total sales
    // Your code here
}

Hint

Use println!("Total sales: {}", total); to show the result.

Practice

1. What does the loop keyword do in Rust?

easy

A. It runs the loop a fixed number of times.

B. It creates an infinite loop that runs until break is called.

C. It runs the loop only once.

D. It creates a loop that runs only if a condition is true.

Solution

1. Step 1: Understand the loop keyword

   The loop keyword in Rust creates a loop that repeats forever unless stopped.

2. Step 2: Identify how to stop the loop

   To stop a loop, you must use break inside it; otherwise, it runs infinitely.

3. Final Answer:

   It creates an infinite loop that runs until break is called. -> Option B

4. Quick Check:

   loop = infinite loop until break [OK]

Hint: Remember: loop runs forever unless broken [OK]

Common Mistakes:

• Thinking loop runs a fixed number of times
• Confusing loop with for or while
• Assuming loop stops automatically

2. Which of the following is the correct syntax to create an infinite loop in Rust?

easy

A. loop { println!("Hello"); }

B. while True { println!("Hello"); }

C. for i in 0.. { println!("Hello"); }

D. repeat { println!("Hello"); }

Solution

1. Step 1: Check Rust syntax for infinite loops

   Rust uses the keyword loop to create an infinite loop.

2. Step 2: Verify each option

   while True { println!("Hello"); } uses while True which is invalid syntax in Rust. for i in 0.. { println!("Hello"); } uses for with an infinite range, but 0.. is not valid without an end. repeat { println!("Hello"); } uses repeat which does not exist in Rust. loop { println!("Hello"); } correctly uses loop.

3. Final Answer:

   loop { println!("Hello"); } -> Option A

4. Quick Check:

   Correct infinite loop syntax = loop [OK]

Hint: Use loop keyword for infinite loops in Rust [OK]

Common Mistakes:

• Using while True which is invalid in Rust
• Trying to use repeat which doesn't exist
• Using for without a proper range

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

B. 0 1 2

C. 1 2 3

D. No output (infinite loop)

Solution

1. Step 1: Trace the loop iterations

   Initially, count = 0. In the first loop, count becomes 1, which is printed. Then count becomes 2 and printed. When count becomes 3, the loop breaks before printing.

2. Step 2: List printed values

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

3. Final Answer:

   1 2 -> Option A

4. Quick Check:

   Loop prints until count == 3, so prints 1 and 2 [OK]

Hint: Check when break happens before printing [OK]

Common Mistakes:

• Printing count after break condition
• Starting count from 0 but expecting 0 to print
• Assuming infinite loop without break

4. Identify the error in this Rust loop code:

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

medium

A. 'println!' macro syntax is wrong.

B. Missing semicolon after 'break'.

C. 'loop' keyword is used incorrectly.

D. Variable 'i' is not incremented, causing an infinite loop.

Solution

1. Step 1: Check loop control variable

   The variable i is initialized but never changed inside the loop.

2. Step 2: Understand loop behavior

   Since i never increments, i == 5 is never true, so break is never reached, causing an infinite loop.

3. Final Answer:

   Variable 'i' is not incremented, causing an infinite loop. -> Option D

4. Quick Check:

   Loop needs variable increment to reach break [OK]

Hint: Always update loop variables to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Assuming break works without condition change
• Misunderstanding loop syntax

5. How can you use a loop to sum numbers from 1 to 5 in Rust?

hard

A. Use loop with a counter but never update sum.

B. Use loop without break and add numbers forever.

C. Use a loop with a counter and break when counter > 5, adding each to sum.

D. Use loop with a counter but break immediately without adding.

Solution

1. Step 1: Plan the loop with counter and sum

   Initialize a counter at 1 and sum at 0. Use loop to add counter to sum.

2. Step 2: Use break to stop after 5

   Increment counter each loop. When counter > 5, use break to exit loop.

3. Step 3: Result is sum of 1 to 5

   This method correctly sums numbers 1+2+3+4+5 = 15.

4. Final Answer:

   Use a loop with a counter and break when counter > 5, adding each to sum. -> Option C

5. Quick Check:

   Loop + counter + break = sum 1 to 5 [OK]

Hint: Increment counter and break after limit to sum [OK]

Common Mistakes:

• Not breaking loop causing infinite sum
• Not incrementing counter
• Not adding counter to sum