Why structs are used in Rust - See It in Action

Why structs are used

📖 Scenario: Imagine you want to keep information about a book in a library. You need to store the book's title, author, and number of pages together.

🎯 Goal: You will create a struct to group related information about a book, then create an instance of that struct and print its details.

📋 What You'll Learn

Create a struct named Book with fields title, author, and pages

Create a variable named my_book of type Book with exact values

Use a variable named book_title to store the title of my_book

Print the book_title variable

💡 Why This Matters

🌍 Real World

Structs help organize data about objects like books, users, or products in programs.

💼 Career

Understanding structs is key for Rust programming jobs, as they are used to model data clearly and safely.

1

Create a struct named Book

Write a struct named Book with three fields: title and author as String, and pages as u32.

Rust

# Your code here

Hint

Use struct Book { title: String, author: String, pages: u32 } to group book details.

2

Create a variable my_book of type Book

Create a variable named my_book of type Book with title set to "The Rust Book", author set to "Steve", and pages set to 550.

Rust

struct Book {
    title: String,
    author: String,
    pages: u32,
}

# Your code here

Hint

Use let my_book = Book { title: String::from("The Rust Book"), author: String::from("Steve"), pages: 550 };

3

Store the title of my_book in book_title

Create a variable named book_title and set it to the title field of my_book.

Rust

struct Book {
    title: String,
    author: String,
    pages: u32,
}

let my_book = Book {
    title: String::from("The Rust Book"),
    author: String::from("Steve"),
    pages: 550,
};

# Your code here

Hint

Use let book_title = &my_book.title; to get the title.

4

Print the book_title

Write a println! statement to print the value of book_title.

Rust

struct Book {
    title: String,
    author: String,
    pages: u32,
}

let my_book = Book {
    title: String::from("The Rust Book"),
    author: String::from("Steve"),
    pages: 550,
};

let book_title = &my_book.title;

# Your code here

Hint

Use println!("{}", book_title); to show the title.

Practice

1. Why do Rust programmers use structs in their code?

easy

A. To group related data together under one name

B. To write faster loops

C. To create functions

D. To handle errors automatically

Solution

1. Step 1: Understand the purpose of structs

   Structs are used to combine multiple pieces of related data into one named unit.

2. Step 2: Compare with other options

   Loops, functions, and error handling are different concepts and not the main reason for structs.

3. Final Answer:

   To group related data together under one name -> Option A

4. Quick Check:

   Structs = Group related data [OK]

Hint: Structs bundle related info like a real-world object [OK]

Common Mistakes:

• Thinking structs are for loops or functions
• Confusing structs with error handling
• Believing structs speed up code automatically

2. Which of the following is the correct way to define a simple struct in Rust?

easy

A. struct Person: { name String, age u32 }

B. struct Person = (name: String, age: u32);

C. struct Person { name: String, age: u32 }

D. struct Person { name; String, age; u32 }

Solution

1. Step 1: Recall Rust struct syntax

   Rust structs use the format: struct Name { field1: Type1, field2: Type2 }.

2. Step 2: Check each option

   struct Person { name: String, age: u32 } matches the correct syntax. Options B, C, and D have syntax errors like wrong punctuation or missing colons.

3. Final Answer:

   struct Person { name: String, age: u32 } -> Option C

4. Quick Check:

   Correct struct syntax = struct Person { name: String, age: u32 } [OK]

Hint: Remember: fields use colon and commas inside braces [OK]

Common Mistakes:

• Using '=' instead of braces
• Missing colons between field names and types
• Using semicolons instead of commas

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

struct Point { x: i32, y: i32 }

fn main() {
    let p = Point { x: 5, y: 10 };
    println!("({}, {})", p.x, p.y);
}

medium

A. Compilation error

B. (5, 10)

C. Point { x: 5, y: 10 }

D. (10, 5)

Solution

1. Step 1: Understand struct field access

   The struct Point has fields x and y. The code creates p with x=5 and y=10.

2. Step 2: Analyze the print statement

   The println! macro prints p.x and p.y in order, so output is (5, 10).

3. Final Answer:

   (5, 10) -> Option B

4. Quick Check:

   Print fields in order = (5, 10) [OK]

Hint: Print fields in order: x then y [OK]

Common Mistakes:

• Swapping x and y values
• Expecting debug print of whole struct
• Thinking code won't compile

4. Identify the error in this Rust struct usage:

struct Car {
    model: String,
    year: u32
}

fn main() {
    let my_car = Car { model: "Tesla", year: "2020" };
}

medium

A. Struct fields must be mutable

B. Missing semicolon after struct definition

C. Model field should be an integer

D. Year field has wrong type: string instead of u32

Solution

1. Step 1: Check struct field types

   The Car struct defines year as u32 (a number).

2. Step 2: Check struct initialization

   The code assigns year: "2020", which is a string, not a number. This causes a type mismatch error.

3. Final Answer:

   Year field has wrong type: string instead of u32 -> Option D

4. Quick Check:

   Field types must match exactly [OK]

Hint: Match field types exactly when creating structs [OK]

Common Mistakes:

• Using quotes around numbers
• Thinking fields must be mutable
• Missing semicolon is not the main error here

5. You want to model a Book with title, author, and number of pages using a Rust struct. Which approach best uses structs to organize this data?

hard

A. Use a struct with fields: title (String), author (String), pages (u32)

B. Use separate variables for title, author, and pages without a struct

C. Use a tuple with (String, String, u32) without naming fields

D. Use a struct with only one field holding all data as a single string

Solution

1. Step 1: Understand the goal of modeling data

   We want to group related properties of a book clearly and access them by name.

2. Step 2: Evaluate options for clarity and organization

   Use a struct with fields: title (String), author (String), pages (u32) uses a struct with named fields for each property, making code clear and organized. Use separate variables for title, author, and pages without a struct scatters data, Use a tuple with (String, String, u32) without naming fields uses unnamed tuple fields, and Use a struct with only one field holding all data as a single string mixes all data into one string, losing structure.

3. Final Answer:

   Use a struct with fields: title (String), author (String), pages (u32) -> Option A

4. Quick Check:

   Structs model real-world things with named properties [OK]

Hint: Use structs to name and group related data clearly [OK]

Common Mistakes:

• Using tuples without field names
• Storing all data in one string
• Avoiding structs and using separate variables