Function declaration in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function named greet that prints a greeting.

Rust

fn [1]() {
    println!("Hello, world!");
}

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

Ahello

Bmain

Cprint

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Using main instead of greet.

Using a keyword like print as a function name.

The function name should be greet to match the task.

2fill in blank

medium

Complete the code to declare a function named add that takes two i32 parameters.

Rust

fn add(a: i32, [1]: i32) -> i32 {
    a + b
}

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

Ab

Bc

Cx

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name different from the one used in the function body.

Using a name not declared as a parameter.

The second parameter name should be b to match the function body.

3fill in blank

hard

Fix the error in the function declaration by completing the missing return type.

Rust

fn multiply(x: i32, y: i32) -> [1] {
    x * y
}

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

Af64

Bbool

Ci32

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using a return type that does not match the expression type.

Omitting the return type when it is required.

The function multiplies two i32 values, so the return type must be i32.

4fill in blank

hard

Fill both blanks to declare a function named is_even that takes an i32 and returns a bool.

Rust

fn [1](num: i32) -> [2] {
    num % 2 == 0
}

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

Ais_even

Bis_odd

Cbool

Di32

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong function name like is_odd.

Using the wrong return type like i32.

The function name is is_even and it returns a bool indicating if the number is even.

5fill in blank

hard

Fill all three blanks to declare a function named describe_number that takes an i32 and returns a String.

Rust

fn [1](n: [2]) -> [3] {
    if n > 0 {
        String::from("Positive")
    } else {
        String::from("Non-positive")
    }
}

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

Adescribe_number

Bi32

CString

Dnumber_desc

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong function name like number_desc.

Using wrong types for parameter or return value.

The function is named describe_number, takes an i32, and returns a String.

Practice

1. What keyword is used to declare a function in Rust?

easy

A. fn

B. function

C. def

D. func

Solution

1. Step 1: Recall Rust function syntax

   In Rust, functions are declared using the keyword fn.

2. Step 2: Compare options with Rust syntax

   Only fn matches the correct Rust keyword for function declaration.

3. Final Answer:

   fn -> Option A

4. Quick Check:

   Function declaration keyword = fn [OK]

Hint: Remember Rust uses 'fn' to start functions [OK]

Common Mistakes:

• Using 'function' instead of 'fn'
• Confusing with Python's 'def'
• Using 'func' which is not Rust syntax

2. Which of the following is the correct syntax to declare a function named greet that takes no parameters and returns nothing in Rust?

easy

A. def greet() {}

B. fn greet() {}

C. fn greet {}

D. function greet() {}

Solution

1. Step 1: Check function declaration syntax

   In Rust, a function with no parameters and no return value is declared as fn name() {}.

2. Step 2: Validate each option

   fn greet() {} matches Rust syntax exactly. Options A and B use keywords from other languages. fn greet {} misses parentheses.

3. Final Answer:

   fn greet() {} -> Option B

4. Quick Check:

   Empty parameter list requires () in Rust [OK]

Hint: Functions always need () even if no parameters [OK]

Common Mistakes:

• Omitting parentheses
• Using other language keywords
• Adding unnecessary keywords

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

fn add(a: i32, b: i32) -> i32 {
    a + b
}

fn main() {
    println!("{}", add(3, 4));
}

medium

A. 7

B. 34

C. a + b

D. Error: missing return

Solution

1. Step 1: Understand the add function

   The function takes two integers and returns their sum using expression a + b.

2. Step 2: Trace the main function call

   Calling add(3, 4) returns 7, which is printed by println!.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Sum of 3 and 4 is 7, printed as output [OK]

Common Mistakes:

• Thinking 'a + b' prints as string
• Concatenating numbers as strings
• Assuming missing return error

4. Identify the error in this Rust function declaration:

fn multiply(x i32, y: i32) -> i32 {
    x * y
}

medium

A. Function name is invalid

B. Missing return type

C. Missing colon after parameter x

D. Missing semicolon after multiplication

Solution

1. Step 1: Check parameter syntax

   Each parameter must have a colon between name and type. Here, x i32 misses the colon.

2. Step 2: Verify other parts

   Return type is present, function name is valid, and semicolon is not needed after expression in Rust.

3. Final Answer:

   Missing colon after parameter x -> Option C

4. Quick Check:

   Parameters need ':' between name and type [OK]

Hint: Parameters need ':' between name and type [OK]

Common Mistakes:

• Omitting colon in parameters
• Adding unnecessary semicolons
• Confusing return type syntax

5. How would you declare a Rust function named is_even that takes an integer parameter and returns a boolean indicating if the number is even?

hard

A. fn is_even(n: i32) -> boolean { n % 2 == 0 }

B. fn is_even(n: i32) { return n % 2 == 0; }

C. fn is_even(n: int) -> bool { n % 2 = 0 }

D. fn is_even(n: i32) -> bool { n % 2 == 0 }

Solution

1. Step 1: Check parameter and return types

   Parameter type must be i32 and return type bool in Rust.

2. Step 2: Validate function body syntax

   Expression n % 2 == 0 correctly returns a boolean. fn is_even(n: i32) -> bool { n % 2 == 0 } uses correct syntax and types.

3. Final Answer:

   fn is_even(n: i32) -> bool { n % 2 == 0 } -> Option D

4. Quick Check:

   Use i32 and bool with correct expression [OK]

Hint: Use '-> bool' and 'n % 2 == 0' for even check [OK]

Common Mistakes:

• Using wrong type names like int or boolean
• Omitting return type
• Using '=' instead of '==' in condition