Using external crates in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add the external crate rand in the Cargo.toml file.

Rust

[dependencies]
rand = "[1]"

Drag options to blanks, or click blank then click option'

Arandom

B1.0

C0.8

Dlatest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'latest' or 'random' as version strings which are invalid.

Omitting the version number.

The rand crate version 0.8 is a valid and commonly used version. You specify the version number as a string in Cargo.toml.

2fill in blank

medium

Complete the code to import the thread_rng function from the rand crate.

Rust

use rand::[1];

Drag options to blanks, or click blank then click option'

ARng

BSeedableRng

Crandom

Dthread_rng

Attempts:

3 left

💡 Hint

Common Mistakes

Importing traits like Rng instead of the function.

Using random which is a different function.

The thread_rng function provides a random number generator local to the current thread.

3fill in blank

hard

Fix the error in the code to generate a random number between 1 and 10.

Rust

let mut rng = thread_rng();
let num = rng.gen_range([1]);

Drag options to blanks, or click blank then click option'

A1..10

B1..=10

C0..10

D1, 10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1..10 which excludes 10.

Passing two numbers separated by a comma which is invalid.

The range 1..=10 includes both 1 and 10, generating numbers from 1 to 10 inclusive.

4fill in blank

hard

Fill both blanks to import the thread_rng function and the Rng trait from the rand crate.

Rust

use rand::[1];
use rand::[2];

Drag options to blanks, or click blank then click option'

Athread_rng

BRng

Crandom

DSeedableRng

Attempts:

3 left

💡 Hint

Common Mistakes

Importing only the function or only the trait.

Importing unrelated items like random or SeedableRng.

You import thread_rng function to get the random number generator and Rng trait to use methods like gen_range.

5fill in blank

hard

Fill all three blanks to create a random number generator, generate a number between 5 and 15, and print it.

Rust

use rand::[1];
use rand::[2];

fn main() {
    let mut rng = [3]();
    let num = rng.gen_range(5..=15);
    println!("Random number: {}", num);
}

Drag options to blanks, or click blank then click option'

Athread_rng

BRng

Drandom

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the function name with the trait name.

Not calling the function to create the generator.

You import thread_rng function and Rng trait, then call thread_rng() to get the generator.

Practice

1. What is the main purpose of using external crates in a Rust project?

easy

A. To make the code run faster automatically

B. To avoid writing any code at all

C. To add extra functionality without writing it yourself

D. To replace the Rust compiler

Solution

1. Step 1: Understand what external crates are

   External crates are packages of code others wrote that you can use in your project.

2. Step 2: Identify their purpose

   They help you add features without coding everything from scratch.

3. Final Answer:

   To add extra functionality without writing it yourself -> Option C

4. Quick Check:

   External crates = add features easily [OK]

Hint: External crates add features you don't code yourself [OK]

Common Mistakes:

• Thinking crates speed up code automatically
• Believing crates replace Rust compiler
• Assuming crates remove all coding

2. Which of the following is the correct way to add an external crate named rand to your Rust project?

easy

A. Add import rand; in main.rs

B. Write use rand; in Cargo.toml

C. Add extern crate rand; in Cargo.toml

D. Add rand = "0.8" under [dependencies] in Cargo.toml

Solution

1. Step 1: Know where to add crate versions

   Crate versions go under [dependencies] in Cargo.toml file.

2. Step 2: Identify correct syntax

   The correct syntax is rand = "0.8" under [dependencies].

3. Final Answer:

   Add rand = "0.8" under [dependencies] in Cargo.toml -> Option D

4. Quick Check:

   Cargo.toml dependencies = rand = "0.8" [OK]

Hint: Add crate and version under [dependencies] in Cargo.toml [OK]

Common Mistakes:

• Trying to use 'use' or 'import' in Cargo.toml
• Writing extern crate in Cargo.toml instead of code
• Adding crate info in main.rs instead of Cargo.toml

3. Given the following code and Cargo.toml setup, what will be the output? Cargo.toml snippet:

[dependencies]
regex = "1"

main.rs snippet:

use regex::Regex;

fn main() {
    let re = Regex::new(r"\d+").unwrap();
    let text = "abc123def";
    println!("{}", re.is_match(text));
}

medium

A. true

B. false

C. Compilation error

D. Runtime panic

Solution

1. Step 1: Understand what the regex checks

   The regex looks for one or more digits (\d+) in the text "abc123def".

2. Step 2: Check if the text contains digits

   The text contains "123", so the regex matches and returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Regex match found = true [OK]

Hint: Regex \d+ matches digits in string, so output true [OK]

Common Mistakes:

• Thinking regex returns false if digits exist
• Expecting compilation error due to crate usage
• Assuming unwrap causes panic here

4. What is wrong with this Rust code using the chrono crate? Cargo.toml:

[dependencies]
chrono = "0.4"

main.rs:

use chrono::DateTime;

fn main() {
    let now = DateTime::now();
    println!("{}", now);
}

medium

A. Missing extern crate chrono declaration

B. DateTime::now() does not exist; use Utc::now() instead

C. Cargo.toml version is incorrect

D. println! macro cannot print DateTime

Solution

1. Step 1: Check DateTime usage

   DateTime::now() is not a valid method; chrono uses Utc::now() to get current time.

2. Step 2: Identify correct method to get current time

   Use chrono::Utc::now() to get current DateTime.

3. Final Answer:

   DateTime::now() does not exist; use Utc::now() instead -> Option B

4. Quick Check:

   Use Utc::now() for current time [OK]

Hint: Use Utc::now(), not DateTime::now() for current time [OK]

Common Mistakes:

• Trying to call DateTime::now() directly
• Forgetting to import chrono::Utc
• Assuming extern crate needed in 2018 edition

5. You want to use the serde_json crate to convert a Rust struct into a JSON string. Which steps are needed to do this correctly?

hard

A. Add serde and serde_json to Cargo.toml, derive Serialize on struct, then call serde_json::to_string

B. Only add serde_json to Cargo.toml and call to_string on struct directly

C. Add serde_json to Cargo.toml and use println!("{}", struct) without Serialize

D. Add serde to Cargo.toml and call struct.to_json() method

Solution

1. Step 1: Add required crates in Cargo.toml

   You must add both serde and serde_json under [dependencies] to use serialization features.

2. Step 2: Derive Serialize trait on your struct

   To convert struct to JSON, it must implement Serialize, usually by adding #[derive(Serialize)].

3. Step 3: Use serde_json::to_string to convert struct

   Call serde_json::to_string(&your_struct) to get JSON string.

4. Final Answer:

   Add serde and serde_json to Cargo.toml, derive Serialize on struct, then call serde_json::to_string -> Option A

5. Quick Check:

   Serialize + serde_json::to_string = JSON string [OK]

Hint: Add serde + serde_json, derive Serialize, then use to_string [OK]

Common Mistakes:

• Forgetting to add serde crate
• Not deriving Serialize on struct
• Trying to call to_string directly on struct