Compound data types in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust tuple code?

Consider the following Rust code using tuples. What will it print?

Rust

fn main() {
    let tup: (i32, f64, u8) = (500, 6.4, 1);
    let (x, y, z) = tup;
    println!("{} {} {}", x, y, z);
}

A 6.4 500 1

B 500 6.4 1

C 500 1 6.4

D Error: cannot print tuple elements directly

💡 Hint

Remember tuple elements keep their order and types.

The tuple tup has elements in order: 500 (i32), 6.4 (f64), and 1 (u8). The pattern (x, y, z) matches them in order. So printing x y z prints 500 6.4 1.

❓ Predict Output

intermediate

What is the output of this Rust array code?

What will this Rust program print?

Rust

fn main() {
    let arr = [10, 20, 30, 40, 50];
    let slice = &arr[1..4];
    println!("{:?}", slice);
}

A [20, 30, 40]

B [10, 20, 30, 40]

C [30, 40, 50]

D Error: cannot slice arrays this way

💡 Hint

Remember Rust slices include the start index but exclude the end index.

The slice &arr[1..4] includes elements at indices 1, 2, and 3, which are 20, 30, 40. The end index 4 is excluded.

🔧 Debug

advanced

Why does this Rust struct code fail to compile?

Look at this Rust code defining and using a struct. Why does it fail to compile?

Rust

struct Point {
    x: i32,
    y: i32,
}

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

A Error because Point struct must derive Debug trait

B Error because struct fields must be mutable

C Error because println! macro syntax is wrong

D Error because field 'y' is missing when creating Point

💡 Hint

Check if all struct fields are initialized when creating an instance.

The struct Point has two fields: x and y. When creating p, only x is given a value. Rust requires all fields to be initialized unless default values or other constructors are used.

❓ Predict Output

advanced

What is the output of this Rust enum and match code?

What will this Rust program print?

Rust

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
}

fn main() {
    let msg = Message::Move { x: 10, y: 20 };
    match msg {
        Message::Quit => println!("Quit message"),
        Message::Move { x, y } => println!("Move to ({}, {})", x, y),
        Message::Write(text) => println!("Write message: {}", text),
    }
}

A Move to (10, 20)

B Quit message

C Write message: Move to (10, 20)

D Error: match arms missing wildcard pattern

💡 Hint

Look at which enum variant is created and matched.

The variable msg is created as Message::Move { x: 10, y: 20 }. The match arm for Message::Move prints Move to (10, 20). Other arms do not run.

🧠 Conceptual

expert

How many elements does this nested tuple contain?

Consider this nested tuple in Rust:

let nested = ((1, 2), (3, (4, 5)));

How many individual integer elements does nested contain?

A 4

B 3

C 5

D 6

💡 Hint

Count all integers inside all inner tuples.

The tuple nested contains two elements: (1, 2) and (3, (4, 5)). The first inner tuple has 2 integers, the second has 1 integer and another tuple with 2 integers. Total is 2 + 1 + 2 = 5 integers.

Practice

1. Which of the following best describes a tuple in Rust?

easy

A. A named collection of fields with the same type.

B. A dynamically sized list of elements all of the same type.

C. A fixed-size collection of values of possibly different types grouped together.

D. A function that returns multiple values.

Solution

1. Step 1: Understand tuple characteristics

   Tuples group multiple values of different types into one fixed-size compound value.

2. Step 2: Compare with other options

   A dynamically sized list of elements all of the same type describes arrays/vecs. A named collection of fields describes structs. A function that returns multiple values is unrelated to tuples.

3. Final Answer:

   A fixed-size collection of values of possibly different types grouped together. -> Option C

4. Quick Check:

   Tuple = fixed-size, mixed types [OK]

Hint: Tuples hold fixed mixed types by position [OK]

Common Mistakes:

• Confusing tuples with arrays (dynamic size, same type)
• Thinking tuples have named fields like structs
• Assuming tuples can change size after creation

2. Which of the following is the correct syntax to define a tuple with an integer and a string in Rust?

easy

A. let my_tuple = [42, "hello"];

B. let my_tuple = (42, "hello");

C. let my_tuple = {42, "hello"};

D. let my_tuple = <42, "hello">;

Solution

1. Step 1: Recall tuple syntax

   Tuples use parentheses () with comma-separated values, e.g., (value1, value2).

2. Step 2: Check each option

   let my_tuple = (42, "hello"); uses parentheses correctly. let my_tuple = [42, "hello"]; uses square brackets (arrays). let my_tuple = {42, "hello"}; uses braces (blocks or structs). let my_tuple = <42, "hello">; uses angle brackets which are invalid here.

3. Final Answer:

   let my_tuple = (42, "hello"); -> Option B

4. Quick Check:

   Tuple syntax uses () [OK]

Hint: Tuples use parentheses () not brackets [] or braces {} [OK]

Common Mistakes:

• Using square brackets [] instead of parentheses ()
• Using braces {} which define blocks or structs
• Using angle brackets <> which are invalid here

3. What is the output of the following Rust code?

let person = ("Alice", 30);
println!("{} is {} years old", person.0, person.1);

medium

A. Alice is 30 years old

B. ("Alice", 30) is {} years old

C. person.0 is person.1 years old

D. Compilation error due to tuple access

Solution

1. Step 1: Understand tuple indexing

   Tuple elements are accessed by position using dot and index, e.g., person.0 is "Alice", person.1 is 30.

2. Step 2: Analyze the println! macro

   The placeholders {} are replaced by person.0 and person.1 values, printing "Alice is 30 years old".

3. Final Answer:

   Alice is 30 years old -> Option A

4. Quick Check:

   Tuple access person.0 and person.1 works [OK]

Hint: Access tuple elements by .0, .1, etc. [OK]

Common Mistakes:

• Trying to access tuple elements by name instead of position
• Confusing tuple with array indexing syntax
• Expecting tuple to print as a whole automatically

4. Identify the error in this Rust struct definition and fix it:

struct Point {
    x: i32,
    y i32,
}

medium

A. Trailing comma after last field is not allowed.

B. Struct fields cannot be integers.

C. Struct names must be lowercase.

D. Missing colon after y in struct field declaration.

Solution

1. Step 1: Check struct field syntax

   Each field must have a name, colon, and type. The field 'y i32' is missing a colon.

2. Step 2: Validate other options

   Fields can be integers (i32). Struct names are PascalCase by convention. Trailing commas are allowed in Rust structs.

3. Final Answer:

   Missing colon after y in struct field declaration. -> Option D

4. Quick Check:

   Field syntax requires colon between name and type [OK]

Hint: Struct fields need name: type syntax [OK]

Common Mistakes:

• Omitting colon between field name and type
• Thinking trailing commas are errors
• Using lowercase struct names (allowed but not idiomatic)

5. Given the struct and tuple below, which code correctly creates a struct instance from the tuple values?

struct Color {
    red: u8,
    green: u8,
    blue: u8,
}

let rgb = (255, 100, 50);

hard

A. let color = Color { red: rgb.0, green: rgb.1, blue: rgb.2 };

B. let color = Color(rgb.0, rgb.1, rgb.2);

C. let color = Color { 255, 100, 50 };

D. let color = (red: 255, green: 100, blue: 50);

Solution

1. Step 1: Understand struct initialization

   Structs with named fields require field names and values in braces, e.g., Color { red: val, green: val, blue: val }.

2. Step 2: Use tuple values correctly

   Tuple elements are accessed by position: rgb.0, rgb.1, rgb.2. let color = Color { red: rgb.0, green: rgb.1, blue: rgb.2 }; uses this correctly.

3. Step 3: Check incorrect options

   let color = Color(rgb.0, rgb.1, rgb.2); uses tuple struct syntax, but Color is not a tuple struct. let color = Color { 255, 100, 50 }; omits field names. let color = (red: 255, green: 100, blue: 50); is invalid syntax.

4. Final Answer:

   let color = Color { red: rgb.0, green: rgb.1, blue: rgb.2 }; -> Option A

5. Quick Check:

   Struct init needs field names with values [OK]

Hint: Use field names when creating structs from tuples [OK]

Common Mistakes:

• Trying to initialize struct without field names
• Using tuple struct syntax for normal structs
• Incorrect syntax for struct initialization