Array basics in Rust - Mini Project: Build & Apply

Array basics

📖 Scenario: You are organizing a small fruit basket. You want to keep track of the fruits you have using an array.

🎯 Goal: Create an array of fruits, count how many fruits you have, and print the list and the count.

📋 What You'll Learn

Create an array called fruits with exactly these values: "Apple", "Banana", "Cherry"

Create a variable called count that stores the number of fruits in the fruits array

Use a for loop with variable fruit to iterate over the fruits array

Print each fruit inside the loop

After the loop, print the total count of fruits using the count variable

💡 Why This Matters

🌍 Real World

Arrays are used to store lists of items like fruits, names, or numbers in many programs.

💼 Career

Understanding arrays is essential for programming jobs because they help organize and manage data efficiently.

1

Create the fruits array

Create an array called fruits with these exact string values: "Apple", "Banana", "Cherry"

Rust

# Your code here

Hint

Use square brackets [] to create an array and separate items with commas.

2

Count the fruits

Create a variable called count that stores the number of items in the fruits array using fruits.len()

Rust

fn main() {
    let fruits = ["Apple", "Banana", "Cherry"];
    
    # Your code here
}

Hint

Use the len() method on the array to get its length.

3

Print each fruit

Use a for loop with variable fruit to iterate over fruits and print each fruit using println!("{}", fruit)

Rust

fn main() {
    let fruits = ["Apple", "Banana", "Cherry"];
    let count = fruits.len();

    # Your code here
}

Hint

Use for fruit in fruits to loop through the array.

4

Print the total count

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

Rust

fn main() {
    let fruits = ["Apple", "Banana", "Cherry"];
    let count = fruits.len();

    for fruit in fruits {
        println!("{}", fruit);
    }

    # Your code here
}

Hint

Use println! to show the total count after the loop.

Practice

1. What is true about arrays in Rust?

easy

A. Their size can change after creation.

B. They store multiple values of the same type in a fixed-size list.

C. They can store values of different types together.

D. They do not allow access by index.

Solution

1. Step 1: Understand array type restrictions

   Arrays in Rust hold values all of the same type, ensuring type safety.

2. Step 2: Understand array size behavior

   Arrays have a fixed size that cannot be changed after creation.

3. Final Answer:

   They store multiple values of the same type in a fixed-size list. -> Option B

4. Quick Check:

   Array = fixed size + same type [OK]

Hint: Remember: Rust arrays are fixed size and single type [OK]

Common Mistakes:

• Thinking arrays can hold mixed types
• Assuming arrays can grow or shrink
• Believing arrays don't use indexes

2. Which of the following is the correct way to declare an array of 3 integers in Rust?

easy

A. let arr = [1, 2, 3];

B. let arr = (1, 2, 3);

C. let arr = {1, 2, 3};

D. let arr = <1, 2, 3>;

Solution

1. Step 1: Identify Rust array syntax

   Arrays use square brackets [] with comma-separated values.

2. Step 2: Check other options

   Parentheses () create tuples, curly braces {} are blocks, angle brackets <> are not valid here.

3. Final Answer:

   let arr = [1, 2, 3]; -> Option A

4. Quick Check:

   Array syntax uses [] [OK]

Hint: Arrays use square brackets [] with commas [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing arrays with tuples
• Using invalid symbols like {} or <>

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

let arr = [10, 20, 30, 40];
println!("{}", arr[2]);

medium

A. Index out of bounds error

B. 20

C. 40

D. 30

Solution

1. Step 1: Understand array indexing

   Rust arrays start indexing at 0, so arr[2] is the third element.

2. Step 2: Identify the element at index 2

   The elements are [10, 20, 30, 40], so arr[2] is 30.

3. Final Answer:

   30 -> Option D

4. Quick Check:

   Index 2 = 30 [OK]

Hint: Count from zero to find the correct index [OK]

Common Mistakes:

• Starting count at 1 instead of 0
• Confusing element positions
• Expecting runtime error for valid index

4. Find the error in this Rust code snippet:

let arr = [1, 2, 3];
println!("{}", arr[3]);

medium

A. No error, prints 3

B. Type mismatch error

C. Index out of bounds error at runtime

D. Syntax error due to missing semicolon

Solution

1. Step 1: Check array length and index used

   The array has 3 elements with indexes 0, 1, 2. Index 3 is invalid.

2. Step 2: Understand Rust runtime behavior

   Accessing arr[3] causes a runtime panic due to index out of bounds.

3. Final Answer:

   Index out of bounds error at runtime -> Option C

4. Quick Check:

   Invalid index causes runtime panic [OK]

Hint: Check if index is less than array length [OK]

Common Mistakes:

• Assuming index 3 is valid for 3-element array
• Confusing syntax error with runtime error
• Ignoring Rust's panic on invalid index

5. You want to create an array of 5 zeros in Rust. Which code correctly does this?

hard

A. let arr = [0; 5];

B. let arr = [0, 5];

C. let arr = [5; 0];

D. let arr = [0] * 5;

Solution

1. Step 1: Understand Rust array repetition syntax

   The syntax [value; count] creates an array repeating value count times.

2. Step 2: Check each option

   let arr = [0; 5]; uses [0; 5], which creates 5 zeros. Others are invalid or create wrong arrays.

3. Final Answer:

   let arr = [0; 5]; -> Option A

4. Quick Check:

   Use [value; count] to repeat values [OK]

Hint: Use [value; count] to make repeated arrays [OK]

Common Mistakes:

• Using commas instead of semicolon for repetition
• Confusing multiplication syntax with arrays
• Reversing value and count in repetition