For loop in Rust - Mini Project: Build & Apply

Using a For Loop in Rust

📖 Scenario: You are helping a small shop owner who wants to list the prices of some fruits they sell. You will write a Rust program to show each fruit and its price.

🎯 Goal: Build a Rust program that uses a for loop to print each fruit and its price from a list.

📋 What You'll Learn

Create a vector called fruits with tuples of fruit names and prices

Create a variable called count to count the number of fruits

Use a for loop with variables name and price to iterate over fruits

Print each fruit name and price inside the loop

Print the total number of fruits after the loop

💡 Why This Matters

🌍 Real World

For loops are used to process lists of items like products, prices, or user data in many programs.

💼 Career

Understanding for loops is essential for software development jobs where you handle collections of data efficiently.

1

Create the fruit list

Create a vector called fruits with these exact tuples: ("Apple", 3), ("Banana", 2), ("Cherry", 5).

Rust

# Create a vector called fruits with tuples of fruit names and prices
# Your code here

Hint

Use let fruits = vec![("Apple", 3), ("Banana", 2), ("Cherry", 5)]; to create the list.

2

Add a count variable

Add a variable called count and set it to 0 to count the fruits.

Rust

fn main() {
    let fruits = vec![("Apple", 3), ("Banana", 2), ("Cherry", 5)];
    // Create a variable count and set it to 0
    // Your code here
}

Hint

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

3

Use a for loop to print fruits

Use a for loop with variables name and price to iterate over fruits.iter(). Inside the loop, print the fruit name and price using println!("{}: ${}", name, price); and increase count by 1.

Rust

fn main() {
    let fruits = vec![("Apple", 3), ("Banana", 2), ("Cherry", 5)];
    let mut count = 0;
    // Use a for loop to print each fruit and price, and increase count
    // Your code here
}

Hint

Use for (name, price) in fruits.iter() to loop. Use count += 1; to add one each time.

4

Print the total count

After the loop, print the total number of fruits using println!("Total fruits: {}", count);.

Rust

fn main() {
    let fruits = vec![("Apple", 3), ("Banana", 2), ("Cherry", 5)];
    let mut count = 0;
    for (name, price) in fruits.iter() {
        println!("{}: ${}", name, price);
        count += 1;
    }
    // Print the total number of fruits
    // Your code here
}

Hint

Use println!("Total fruits: {}", count); after the loop to show the count.

Practice

1. What does a for loop do in Rust?

easy

A. Declares a variable

B. Defines a new function

C. Repeats actions for each item in a collection

D. Stops the program immediately

Solution

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

   A for loop runs code repeatedly for each item in a list or range.

2. Step 2: Match the description to the options

   Only Repeats actions for each item in a collection describes repeating actions over items in a collection.

3. Final Answer:

   Repeats actions for each item in a collection -> Option C

4. Quick Check:

   For loop = repeat over items [OK]

Hint: For loops repeat actions over collections [OK]

Common Mistakes:

• Confusing for loop with function definition
• Thinking for loop declares variables
• Believing for loop stops program

2. Which of these is the correct syntax for a for loop iterating over numbers 1 to 3 in Rust?

easy

A. for i = 1 to 3 { println!("{}", i); }

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

C. for (i in 1..3) println!("{}", i);

D. for i in range(1,3) { println!("{}", i); }

Solution

1. Step 1: Recall Rust for loop syntax

   Rust uses for variable in range { } with ranges like 1..=3 to include 3.

2. Step 2: Check each option

   for i in 1..=3 { println!("{}", i); } uses correct Rust syntax with inclusive range. Others use invalid syntax or functions not in Rust.

3. Final Answer:

   for i in 1..=3 { println!("{}", i); } -> Option B

4. Quick Check:

   Rust for loop uses in and ranges [OK]

Hint: Use 'for var in start..=end' for inclusive ranges [OK]

Common Mistakes:

• Using 'to' instead of 'in' keyword
• Using parentheses around loop variable
• Using Python or other language range syntax

3. What is the output of this Rust code?

let mut sum = 0;
for i in 1..4 {
    sum += i;
}
println!("{}", sum);

medium

A. 6

B. 10

C. 9

D. 7

Solution

1. Step 1: Identify the loop range and iterations

   The loop runs for i = 1, 2, 3 because 1..4 excludes 4.

2. Step 2: Calculate the sum of iterations

   sum = 0 + 1 + 2 + 3 = 6

3. Final Answer:

   6 -> Option A

4. Quick Check:

   1+2+3 = 6 [OK]

Hint: Remember range excludes the end number [OK]

Common Mistakes:

• Including 4 in the sum
• Starting sum at 1 instead of 0
• Confusing inclusive and exclusive ranges

4. Find the error in this Rust for loop code:

for i in 0..5
    println!("{}", i);
}

medium

A. Variable i is not declared

B. Range syntax is incorrect

C. println! macro is used incorrectly

D. Missing curly braces around loop body

Solution

1. Step 1: Check loop syntax

   Rust requires curly braces { } around the loop body if it has more than one statement or to be explicit.

2. Step 2: Identify the missing brace

   The code has a closing brace '}' without an opening brace '{' before println!().

3. Final Answer:

   Missing curly braces around loop body -> Option D

4. Quick Check:

   For loop body needs braces [OK]

Hint: Always use braces {} for loop bodies [OK]

Common Mistakes:

• Forgetting opening brace
• Assuming range syntax is wrong
• Thinking variable needs declaration outside loop

5. How can you use a for loop in Rust to print only even numbers from 2 to 10 inclusive?

hard

A. for i in 2..=10 { if i % 2 == 0 { println!("{}", i); } }

B. for i in 2..10 { if i % 2 = 0 { println!("{}", i); } }

C. for i in 2..=10 { if i / 2 == 0 { println!("{}", i); } }

D. for i in 2..=10 { if i % 2 != 0 { println!("{}", i); } }

Solution

1. Step 1: Understand the range and condition

   We want numbers from 2 to 10 inclusive, so use 2..=10. To print even numbers, check if remainder when divided by 2 is zero.

2. Step 2: Check each option's condition

   for i in 2..=10 { if i % 2 == 0 { println!("{}", i); } } correctly uses i % 2 == 0. for i in 2..10 { if i % 2 = 0 { println!("{}", i); } } uses assignment (=) instead of comparison (==). for i in 2..=10 { if i / 2 == 0 { println!("{}", i); } } uses division instead of modulo. for i in 2..=10 { if i % 2 != 0 { println!("{}", i); } } prints odd numbers.

3. Final Answer:

   for i in 2..=10 { if i % 2 == 0 { println!("{}", i); } } -> Option A

4. Quick Check:

   Use modulo == 0 for even check [OK]

Hint: Use 'if i % 2 == 0' inside for loop [OK]

Common Mistakes:

• Using '=' instead of '==' in condition
• Using division instead of modulo
• Printing odd numbers by mistake