Basic match usage in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust code using match?

Look at this Rust program. What will it print when run?

Rust

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

A Two

B Other

C One

D Three

💡 Hint

Check which pattern matches the value 3 in the match expression.

The variable 'number' is 3, so the match arm '3 => println!("Three")' runs, printing 'Three'.

❓ Predict Output

intermediate

What does this Rust match expression return?

What value does this Rust code assign to 'result'?

Rust

fn main() {
    let x = 5;
    let result = match x {
        1..=4 => "small",
        5..=10 => "medium",
        _ => "large",
    };
    println!("{}", result);
}

A medium

B small

C large

D Compilation error

💡 Hint

Look at the range patterns and see where 5 fits.

The value 5 matches the range 5..=10, so 'medium' is assigned to 'result'.

❓ Predict Output

advanced

What is the output of this nested match in Rust?

Analyze the nested match statements and find the output.

Rust

fn main() {
    let a = Some(2);
    let b = 3;
    match a {
        Some(x) => match b {
            3 => println!("x is {} and b is three", x),
            _ => println!("x is {} and b is not three", x),
        },
        None => println!("No value for a"),
    }
}

A No value for a

B x is 2 and b is three

C x is 2 and b is not three

D Compilation error

💡 Hint

Check the values inside the nested match carefully.

Variable 'a' is Some(2), so first match arm runs. Then 'b' is 3, so inner match prints 'x is 2 and b is three'.

❓ Predict Output

advanced

What error does this Rust code produce?

What error will this Rust code cause when compiled?

Rust

fn main() {
    let num = 7;
    match num {
        1 => println!("One"),
        2 => println!("Two"),
        _ => (),
    }
}

A Error: variable 'num' not found

B Error: mismatched types

C Error: non-exhaustive patterns in match

D No error, prints nothing

💡 Hint

Think about what happens if 'num' is 7 and no match arm covers it.

The match is not exhaustive because it only covers 1 and 2, but 'num' is 7. Rust requires all cases covered or a wildcard '_'.

🧠 Conceptual

expert

How many arms does this Rust match expression have?

Count the number of arms in this Rust match expression.

Rust

fn main() {
    let val = 10;
    match val {
        1 | 2 | 3 => println!("One, two or three"),
        4..=10 => println!("Between four and ten"),
        _ => println!("Something else"),
    }
}

A 3

B 2

C 4

D 5

💡 Hint

Count each separate match arm, not the number of values in patterns.

There are three arms: one for 1|2|3, one for 4..=10, and one wildcard '_'.

Practice

1. What does the match expression do in Rust?

easy

A. It compares a value against multiple patterns and runs matching code.

B. It creates a new variable with a fixed value.

C. It loops through a list of numbers.

D. It defines a function that returns a value.

Solution

1. Step 1: Understand the purpose of match

   The match expression compares a value against several patterns.

2. Step 2: Identify what happens on a match

   When a pattern matches, the corresponding code block runs.

3. Final Answer:

   It compares a value against multiple patterns and runs matching code. -> Option A

4. Quick Check:

   match checks patterns = C [OK]

Hint: Remember: match checks value patterns and runs matching code [OK]

Common Mistakes:

• Thinking match creates variables
• Confusing match with loops
• Believing match defines functions

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

easy

A. match value { pattern : action, _ : default_action }

B. match (value) { pattern -> action, _ -> default_action }

C. match value { pattern => action, _ => default_action }

D. match value (pattern => action, _ => default_action)

Solution

1. Step 1: Recall Rust match syntax

   Rust uses curly braces with patterns and arrows: { pattern => action }.

2. Step 2: Check each option's syntax

   match value { pattern => action, _ => default_action } matches Rust syntax exactly; others use wrong symbols or parentheses.

3. Final Answer:

   match value { pattern => action, _ => default_action } -> Option C

4. Quick Check:

   Correct match syntax = A [OK]

Hint: Look for curly braces and => arrows in match syntax [OK]

Common Mistakes:

• Using parentheses instead of braces
• Using -> instead of =>
• Using colons instead of arrows

3. What is 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.

2. Step 2: Find matching pattern in match arms

   The pattern 3 matches, so it prints "Three".

3. Final Answer:

   Three -> Option D

4. Quick Check:

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

Hint: Match value to pattern exactly to find output [OK]

Common Mistakes:

• Choosing default (_) arm instead of exact match
• Confusing numbers in patterns
• Ignoring the value of the variable

4. Find the error in this Rust code snippet:

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

medium

A. Missing semicolon after println! macros

B. Missing default (_) arm to cover other values

C. Incorrect variable name in match

D. Using parentheses instead of braces in match

Solution

1. Step 1: Check match arms coverage

   The match covers only 1, 2, and 3 but variable is 5.

2. Step 2: Identify missing default arm

   Without a _ arm, the code will not compile because not all values are covered.

3. Final Answer:

   Missing default (_) arm to cover other values -> Option B

4. Quick Check:

   All values must be matched or _ arm added [OK]

Hint: Always add _ arm to cover unmatched cases [OK]

Common Mistakes:

• Assuming semicolons are required after println!
• Ignoring missing default arm errors
• Confusing variable names

5. You want to write a match expression that returns a string describing a number: "small" for 1 or 2, "medium" for 3 or 4, and "large" for any other number. Which code correctly uses match to do this?

hard

A. match num {
1 | 2 => "small",
3 | 4 => "medium",
_ => "large",
}

B. match num {
1, 2 => "small",
3, 4 => "medium",
_ => "large",
}

C. match num {
1 || 2 => "small",
3 || 4 => "medium",
_ => "large",
}

D. match num {
[1, 2] => "small",
[3, 4] => "medium",
_ => "large",
}

Solution

1. Step 1: Understand pattern alternatives in match

   Rust uses | to match multiple patterns in one arm.

2. Step 2: Check each option's pattern syntax

   match num { 1 | 2 => "small", 3 | 4 => "medium", _ => "large", } correctly uses 1 | 2 and 3 | 4. Others use invalid syntax like commas, ||, or arrays.

3. Final Answer:

   match num { 1 | 2 => "small", 3 | 4 => "medium", _ => "large", } -> Option A

4. Quick Check:

   Use | for multiple patterns in match arms [OK]

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

Common Mistakes:

• Using commas instead of | in patterns
• Using || which is logical OR, not pattern OR
• Trying to match arrays instead of values