Match overview in Rust - Mini Project: Build & Apply

Match Overview

📖 Scenario: You are building a simple program to describe the weather using Rust's match expression. This helps you choose a message based on the weather condition.

🎯 Goal: Create a Rust program that uses a match expression to print a message about the weather condition.

📋 What You'll Learn

Create a variable called weather with the value "sunny"

Create a variable called message that uses a match expression on weather

Use match arms for "sunny", "rainy", and a default arm

Print the message variable

💡 Why This Matters

🌍 Real World

Using <code>match</code> expressions helps programs make decisions based on different inputs, like choosing messages or actions depending on conditions.

💼 Career

Understanding <code>match</code> is important for Rust programming jobs, especially when handling different cases clearly and safely.

1

Create the weather variable

Create a variable called weather and set it to the string "sunny".

Rust

# Create a variable called weather and set it to "sunny"
// Your code here

Hint

Use let to create a variable and assign the string "sunny".

2

Create the message variable with match

Create a variable called message that uses a match expression on weather. Use arms for "sunny" and "rainy" that return appropriate messages, and a default arm that returns "Unknown weather".

Rust

fn main() {
    let weather = "sunny";
    // Create a variable called message using match on weather
    // Your code here
}

Hint

Use match weather { ... } and include arms for "sunny", "rainy", and a default arm _.

3

Add a print statement to show the message

Add a println! statement to print the message variable.

Rust

fn main() {
    let weather = "sunny";
    let message = match weather {
        "sunny" => "It is a bright and sunny day!",
        "rainy" => "It is raining outside.",
        _ => "Unknown weather",
    };
    // Print the message variable
    // Your code here
}

Hint

Use println!("{}", message); to display the message.

4

Run the program and see the output

Run the program to see the printed message about the weather.

Rust

fn main() {
    let weather = "sunny";
    let message = match weather {
        "sunny" => "It is a bright and sunny day!",
        "rainy" => "It is raining outside.",
        _ => "Unknown weather",
    };
    println!("{}", message);
}

// Run the program to see the output

Hint

Check the console output after running the program.

Practice

1. What is the main purpose of the match statement in Rust?

easy

A. To check a value against multiple patterns clearly and concisely

B. To create loops that run a fixed number of times

C. To define new data types

D. To handle errors using exceptions

Solution

1. Step 1: Understand the role of match

   The match statement compares a value against many patterns, making code clearer than many if-else statements.

2. Step 2: Compare with other options

   Loops run repeatedly, data types define structures, and exceptions handle errors, but match is for pattern matching.

3. Final Answer:

   To check a value against multiple patterns clearly and concisely -> Option A

4. Quick Check:

   Match = pattern checking [OK]

Hint: Match replaces many if-else with clear pattern checks [OK]

Common Mistakes:

• Confusing match with loops
• Thinking match defines types
• Assuming match handles exceptions

2. Which of the following is the correct syntax for a match expression in Rust?

easy

A. match value { pattern1 => expr1, pattern2 => expr2, _ => default_expr }

B. match (value) { pattern1: expr1; pattern2: expr2; default: default_expr }

C. match value { pattern1 -> expr1, pattern2 -> expr2, _ -> default_expr }

D. match value { pattern1 => expr1; pattern2 => expr2; _ => default_expr }

Solution

1. Step 1: Recall Rust match syntax

   Rust uses curly braces with patterns followed by => and expressions separated by commas.

2. Step 2: Check each option

   match value { pattern1 => expr1, pattern2 => expr2, _ => default_expr } uses correct braces, arrows, and commas. Options B and D use semicolons incorrectly. match value { pattern1 -> expr1, pattern2 -> expr2, _ -> default_expr } uses -> instead of =>.

3. Final Answer:

   match value { pattern1 => expr1, pattern2 => expr2, _ => default_expr } -> Option A

4. Quick Check:

   Correct match syntax uses => and commas [OK]

Hint: Use => between pattern and expression, separate arms with commas [OK]

Common Mistakes:

• Using semicolons instead of commas
• Using -> instead of =>
• Missing the catch-all _ pattern

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

let number = 3;
match number {
    1 => println!("One"),
    2 => println!("Two"),
    3 => println!("Three"),
    _ => println!("Other"),
}

medium

A. One

B. Two

C. Other

D. Three

Solution

1. Step 1: Identify the matched value

   The variable number is 3, so the match will look for pattern 3.

2. Step 2: Find the matching arm

   The arm 3 => println!("Three") matches and prints "Three".

3. Final Answer:

   Three -> Option D

4. Quick Check:

   number=3 matches 3 => "Three" [OK]

Hint: Match value exactly to print correct output [OK]

Common Mistakes:

• Choosing default _ arm instead of exact match
• Confusing numbers with strings
• Ignoring the value of number

4. Identify the error in this Rust match code snippet:

let x = 5;
match x {
    1 => println!("One"),
    2 => println!("Two"),
    3 => println!("Three")
}

medium

A. Missing semicolon after println! macros

B. Using parentheses instead of curly braces in match

C. Missing catch-all _ pattern to handle other values

D. Incorrect variable declaration

Solution

1. Step 1: Check match arms completeness

   The match covers 1, 2, and 3 but does not handle other values like 5.

2. Step 2: Understand Rust match requirements

   Rust requires all possible values to be covered, usually by a catch-all _ pattern.

3. Final Answer:

   Missing catch-all _ pattern to handle other values -> Option C

4. Quick Check:

   Always include _ to cover unmatched cases [OK]

Hint: Always add _ arm to handle unexpected values [OK]

Common Mistakes:

• Forgetting the catch-all _ pattern
• Thinking semicolons are mandatory after println!
• Confusing braces with parentheses

5. Given this Rust code, what will be the output?

let grade = 'B';
match grade {
    'A' | 'B' | 'C' => println!("Pass"),
    'D' => println!("Conditional Pass"),
    _ => println!("Fail"),
}

hard

A. Conditional Pass

B. Pass

C. Fail

D. Compilation error

Solution

1. Step 1: Identify the value and patterns

   The variable grade is 'B'. The first arm matches 'A', 'B', or 'C'.

2. Step 2: Determine which arm runs

   Since 'B' matches the first arm, it prints "Pass".

3. Final Answer:

   Pass -> Option B

4. Quick Check:

   Multiple patterns with | match 'B' => "Pass" [OK]

Hint: Use | to match multiple patterns in one arm [OK]

Common Mistakes:

• Assuming only single pattern per arm
• Choosing wrong output for 'B'
• Thinking code causes compilation error