Accessing elements in Rust - Mini Project: Build & Apply

Accessing elements

📖 Scenario: You are managing a small fruit basket in a kitchen. You want to check which fruits are inside and pick one to eat.

🎯 Goal: Learn how to access elements in a Rust vector by index.

📋 What You'll Learn

Create a vector called fruits with these exact strings: "apple", "banana", "cherry"

Create a variable called index and set it to 1

Access the fruit at position index in the fruits vector and store it in a variable called selected_fruit

Print the selected_fruit to the console

💡 Why This Matters

🌍 Real World

Accessing elements by index is common when working with lists of items, like selecting a product from a shopping list or a song from a playlist.

💼 Career

Many programming jobs require working with collections of data and retrieving specific items efficiently.

1

Create the fruit basket

Create a vector called fruits with these exact strings: "apple", "banana", "cherry"

Rust

# Create a vector called fruits with "apple", "banana", "cherry"
# Your code here

Hint

Use vec!["apple", "banana", "cherry"] to create the vector.

2

Set the index to access

Create a variable called index and set it to 1

Rust

fn main() {
    let fruits = vec!["apple", "banana", "cherry"];
    // Create a variable called index and set it to 1
    // Your code here
}

Hint

Use let index = 1; to create the variable.

3

Access the fruit at the index

Access the fruit at position index in the fruits vector and store it in a variable called selected_fruit

Rust

fn main() {
    let fruits = vec!["apple", "banana", "cherry"];
    let index = 1;
    // Access the fruit at index and store in selected_fruit
    // Your code here
}

Hint

Use let selected_fruit = fruits[index]; to get the fruit.

4

Print the selected fruit

Print the selected_fruit to the console using println!

Rust

fn main() {
    let fruits = vec!["apple", "banana", "cherry"];
    let index = 1;
    let selected_fruit = fruits[index];
    // Print selected_fruit
    // Your code here
}

Hint

Use println!("{}", selected_fruit); to print the fruit.

Practice

1. In Rust, how do you access the first element of an array named arr?

easy

A. arr[0]

B. arr[1]

C. arr.first()

D. arr.get(1)

Solution

1. Step 1: Understand Rust indexing

   Rust arrays and slices use zero-based indexing, so the first element is at index 0.

2. Step 2: Access the element using square brackets

   Using arr[0] accesses the first element directly.

3. Final Answer:

   arr[0] -> Option A

4. Quick Check:

   First element index = 0 [OK]

Hint: Remember: Rust arrays start at index 0 [OK]

Common Mistakes:

• Using index 1 for the first element
• Confusing .first() with indexing
• Using get(1) which accesses second element

2. Which of the following is the correct syntax to access the third element of a vector v in Rust?

easy

A. v.get[3]

B. v(3)

C. v[3]

D. v[2]

Solution

1. Step 1: Recall zero-based indexing

   The third element is at index 2 because counting starts at zero.

2. Step 2: Use square brackets with index 2

   The correct syntax is v[2] to access the third element.

3. Final Answer:

   v[2] -> Option D

4. Quick Check:

   Third element index = 2 [OK]

Hint: Count from zero: third element is index 2 [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using index 3 for third element
• Incorrect method call syntax like get[3]

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

let arr = [10, 20, 30, 40];
println!("{}", arr[1]);

medium

A. 20

B. 40

C. 30

D. 10

Solution

1. Step 1: Identify the array elements and their indexes

   The array arr has elements: 10 at index 0, 20 at index 1, 30 at index 2, and 40 at index 3.

2. Step 2: Access element at index 1

   The code prints arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Index 1 means second element in Rust arrays [OK]

Common Mistakes:

• Printing arr[0] instead of arr[1]
• Confusing index with element value
• Expecting output 30 or 40

4. Consider this Rust code snippet:

let v = vec![1, 2, 3];
let x = v[3];

What is the problem here?

medium

A. Syntax error: wrong vector declaration

B. Index out of bounds panic at runtime

C. Compile-time error: invalid index

D. No problem, x will be 3

Solution

1. Step 1: Check vector size and index used

   The vector v has 3 elements at indexes 0, 1, and 2. Index 3 is out of range.

2. Step 2: Understand Rust's runtime behavior

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

3. Final Answer:

   Index out of bounds panic at runtime -> Option B

4. Quick Check:

   Invalid index causes panic [OK]

Hint: Index must be less than vector length [OK]

Common Mistakes:

• Thinking it causes compile error
• Assuming x will be 3
• Ignoring runtime panic possibility

5. You have a nested vector let data = vec![vec![1, 2], vec![3, 4], vec![5, 6]];. How do you access the number 4?

hard

A. data[0][1]

B. data[2][0]

C. data[1][1]

D. data[1][0]

Solution

1. Step 1: Identify the outer and inner indexes

   The outer vector has 3 inner vectors: index 0 is [1, 2], index 1 is [3, 4], index 2 is [5, 6].

2. Step 2: Access the inner element 4

   Within the inner vector at index 1 ([3, 4]), the element 4 is at index 1.

3. Final Answer:

   data[1][1] -> Option C

4. Quick Check:

   Nested access: outer 1, inner 1 = 4 [OK]

Hint: First index outer vec, second index inner vec [OK]

Common Mistakes:

• Mixing up outer and inner indexes
• Using wrong inner index for element 4
• Accessing out-of-range indexes