Vector vs array comparison in Rust - Hands-On Comparison

Vector vs Array Comparison in Rust

📖 Scenario: You are working on a small Rust program that needs to compare two collections of numbers. One collection is a fixed-size array, and the other is a dynamic vector. You want to check if they contain the same numbers in the same order.

🎯 Goal: Build a Rust program that creates an array and a vector with the same numbers, compares them, and prints whether they are equal or not.

📋 What You'll Learn

Create a fixed-size array called numbers_array with the values [10, 20, 30, 40, 50].

Create a vector called numbers_vector with the values vec![10, 20, 30, 40, 50].

Compare numbers_array and numbers_vector for equality.

Print "Equal" if they are the same, otherwise print "Not equal".

💡 Why This Matters

🌍 Real World

Comparing fixed-size and dynamic collections is common when processing data that may come from different sources or formats.

💼 Career

Understanding how to work with arrays and vectors and compare them is important for Rust developers working on performance-sensitive or data-processing applications.

1

Create the fixed-size array

Create a fixed-size array called numbers_array with these exact values: [10, 20, 30, 40, 50].

Rust

# Create the fixed-size array called numbers_array
# Your code here

Hint

Use square brackets [] to create an array with fixed values.

2

Create the vector

Create a vector called numbers_vector with these exact values: vec![10, 20, 30, 40, 50].

Rust

let numbers_array = [10, 20, 30, 40, 50];
# Create the vector called numbers_vector
# Your code here

Hint

Use vec![...] macro to create a vector with values.

3

Compare the array and vector

Write a let statement to create a boolean variable called are_equal that compares numbers_array and numbers_vector for equality using ==.

Rust

let numbers_array = [10, 20, 30, 40, 50];
let numbers_vector = vec![10, 20, 30, 40, 50];
# Compare numbers_array and numbers_vector for equality and store in are_equal
# Your code here

Hint

Convert the vector to a slice using .as_slice() before comparing to the array.

4

Print the comparison result

Write a println! statement that prints "Equal" if are_equal is true, otherwise prints "Not equal".

Rust

let numbers_array = [10, 20, 30, 40, 50];
let numbers_vector = vec![10, 20, 30, 40, 50];
let are_equal = numbers_array == numbers_vector.as_slice();
# Print "Equal" if are_equal is true, else print "Not equal"
# Your code here

Hint

Use an if statement to check are_equal and print the correct message.

Practice

1. Which of the following statements correctly describes the main difference between a Rust array and a Rust vector?

easy

A. Arrays have a fixed size known at compile time, while vectors can grow or shrink at runtime.

B. Vectors have a fixed size known at compile time, while arrays can grow or shrink at runtime.

C. Both arrays and vectors have fixed sizes and cannot change after creation.

D. Arrays are only used for strings, while vectors are used for numbers.

Solution

1. Step 1: Understand array size behavior

   Arrays in Rust have a fixed size that must be known when the program is compiled.

2. Step 2: Understand vector size behavior

   Vectors are dynamic and can grow or shrink during program execution.

3. Final Answer:

   Arrays have a fixed size known at compile time, while vectors can grow or shrink at runtime. -> Option A

4. Quick Check:

   Array fixed size, Vector dynamic size = C [OK]

Hint: Remember: arrays fixed size, vectors flexible size [OK]

Common Mistakes:

• Confusing which type is fixed or dynamic
• Thinking vectors are fixed size
• Assuming arrays can grow dynamically

2. Which of the following is the correct syntax to declare a vector of integers in Rust?

easy

A. let v = (1, 2, 3);

B. let v = [1, 2, 3];

C. let v = vector(1, 2, 3);

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

Solution

1. Step 1: Identify vector creation syntax

   In Rust, vectors are created using the macro vec![...] with square brackets and exclamation mark.

2. Step 2: Compare options

   let v = vec![1, 2, 3]; uses vec![1, 2, 3], which is correct. let v = [1, 2, 3]; is an array, C and D are invalid syntax for vectors.

3. Final Answer:

   let v = vec![1, 2, 3]; -> Option D

4. Quick Check:

   Vector syntax uses vec! macro = A [OK]

Hint: Vectors use vec! macro with square brackets [OK]

Common Mistakes:

• Using array syntax instead of vec! macro
• Missing exclamation mark in vec! macro
• Using parentheses instead of brackets

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

let arr = [10, 20, 30];
let vec = vec![10, 20, 30];
println!("{} {}", arr.len(), vec.len());

medium

A. 3 0

B. 3 3

C. 0 3

D. Compilation error

Solution

1. Step 1: Check array length

   The array arr has 3 elements, so arr.len() returns 3.

2. Step 2: Check vector length

   The vector vec also has 3 elements, so vec.len() returns 3.

3. Final Answer:

   3 3 -> Option B

4. Quick Check:

   Both lengths are 3 = B [OK]

Hint: Both array and vector have length 3 here [OK]

Common Mistakes:

• Assuming vector length is zero initially
• Confusing array and vector length methods
• Expecting compilation error due to different types

4. Identify the error in this Rust code snippet:

let arr = [1, 2, 3];
arr.push(4);

medium

A. Arrays do not have a push method; only vectors do.

B. The array is missing a semicolon after declaration.

C. The push method requires a mutable reference to the array.

D. The code is correct and will compile.

Solution

1. Step 1: Check array methods

   Arrays in Rust have fixed size and do not support the push method.

2. Step 2: Understand push method usage

   The push method is only available for vectors, which are growable.

3. Final Answer:

   Arrays do not have a push method; only vectors do. -> Option A

4. Quick Check:

   push() only works on vectors = D [OK]

Hint: Only vectors support push(), arrays do not [OK]

Common Mistakes:

• Trying to push to arrays
• Thinking arrays can be resized
• Ignoring method availability on types

5. You want to store a list of user scores that can change size during the program. Which Rust type should you choose and why?

hard

A. Use a tuple because it can hold multiple types of scores.

B. Use an array because it is faster and fixed size is better for scores.

C. Use a vector because it can grow or shrink as scores are added or removed.

D. Use a string because scores are numbers stored as text.

Solution

1. Step 1: Analyze data size requirement

   The list of user scores can change size, so a fixed size container is not suitable.

2. Step 2: Choose appropriate Rust type

   Vectors are growable and flexible, making them ideal for dynamic lists like scores.

3. Final Answer:

   Use a vector because it can grow or shrink as scores are added or removed. -> Option C

4. Quick Check:

   Dynamic list needs vector = A [OK]

Hint: Dynamic size needs vector, fixed size needs array [OK]

Common Mistakes:

• Choosing array for dynamic data
• Confusing tuples with lists
• Using string for numeric data