Function call flow in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the function greet.

Rust

fn greet() {
    println!("Hello!");
}

fn main() {
    [1];
}

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

Agreet()

Bgreet

Cprintln!("Hello!")

Dfn greet()

Attempts:

3 left

💡 Hint

Common Mistakes

Writing the function name without parentheses.

Trying to call the function with 'fn' keyword.

To call a function in Rust, you write its name followed by parentheses: greet().

2fill in blank

medium

Complete the code to pass the argument name to the function greet.

Rust

fn greet(name: &str) {
    println!("Hello, {}!", name);
}

fn main() {
    greet([1]);
}

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

Aname

B"Alice"

CAlice

D&name

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an unquoted name which is undefined.

Passing a variable without defining it.

When passing a string literal to a function expecting &str, use quotes: "Alice".

3fill in blank

hard

Fix the error in the function call by completing the blank.

Rust

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

fn main() {
    let sum = add([1]);
    println!("Sum is {}", sum);
}

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

Aadd(5, 3)

B5

C(5, 3)

D5, 3

Attempts:

3 left

💡 Hint

Common Mistakes

Passing only one argument.

Passing a tuple instead of separate arguments.

The function add expects two arguments separated by a comma: 5, 3.

4fill in blank

hard

Fill both blanks to create a function multiply that returns the product of two numbers and call it correctly.

Rust

fn [1](x: i32, y: i32) -> i32 {
    x [2] y
}

fn main() {
    let result = multiply(4, 5);
    println!("Result is {}", result);
}

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

Amultiply

B+

C*

Dmultiply_numbers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong operator like +.

Naming the function differently than the call.

The function name should be multiply and the operator for multiplication is *.

5fill in blank

hard

Fill all three blanks to define a function is_even that returns true if a number is even, and call it with 8.

Rust

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

fn main() {
    let check = [3](8);
    println!("Is even? {}", check);
}

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

Ais_odd

B%

Cis_even

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong function name.

Using wrong operator like / instead of %.

The function name is is_even, the modulo operator is %, and the call uses is_even.

Practice

1. What happens when a function is called in Rust?

easy

A. The program runs the function's code and then returns to the call point.

B. The program skips the function's code and continues after the call.

C. The function code runs only if called twice.

D. The program stops running after the function call.

Solution

1. Step 1: Understand function call behavior

   When a function is called, the program jumps to the function's code and executes it.

2. Step 2: Return to the call point

   After the function finishes, the program returns to the line after the call and continues running.

3. Final Answer:

   The program runs the function's code and then returns to the call point. -> Option A

4. Quick Check:

   Function call flow = run code then return [OK]

Hint: Function calls run code then return to caller [OK]

Common Mistakes:

• Thinking function code is skipped
• Believing program stops after call
• Assuming function runs only if called twice

2. Which of these is the correct way to call a function named greet in Rust?

easy

A. call greet;

B. greet();

C. greet[];

D. function greet();

Solution

1. Step 1: Recall Rust function call syntax

   Functions are called by writing their name followed by parentheses, even if no arguments are passed.

2. Step 2: Match the correct syntax

   Only greet(); matches this pattern correctly.

3. Final Answer:

   greet(); -> Option B

4. Quick Check:

   Function call syntax = name + () [OK]

Hint: Use functionName() to call functions in Rust [OK]

Common Mistakes:

• Omitting parentheses when calling functions
• Using brackets [] instead of parentheses
• Using keywords like 'call' or 'function' incorrectly

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

fn add_one(x: i32) -> i32 {
    x + 1
}

fn main() {
    let result = add_one(5);
    println!("{}", result);
}

medium

A. 5

B. Error: missing semicolon

C. 6

D. 0

Solution

1. Step 1: Understand the function behavior

   The function add_one takes an integer and returns that integer plus one.

2. Step 2: Trace the function call and output

   Calling add_one(5) returns 6, which is printed by println!.

3. Final Answer:

   6 -> Option C

4. Quick Check:

   5 + 1 = 6 [OK]

Hint: Follow function return values to find output [OK]

Common Mistakes:

• Confusing input and output values
• Thinking semicolon causes error here
• Assuming function prints instead of returns

4. Identify the error in this Rust code snippet:

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

fn main() {
    let result = multiply(4);
    println!("{}", result);
}

medium

A. Function multiply is missing a return statement.

B. Variable result is not declared.

C. println! macro is used incorrectly.

D. multiply is called with wrong number of arguments.

Solution

1. Step 1: Check function definition parameters

   The function multiply requires two arguments: x and y.

2. Step 2: Check function call arguments

   The call multiply(4) provides only one argument, causing an error.

3. Final Answer:

   multiply is called with wrong number of arguments. -> Option D

4. Quick Check:

   Function call args must match definition [OK]

Hint: Match function call arguments to definition [OK]

Common Mistakes:

• Ignoring argument count mismatch
• Thinking missing return causes error here
• Assuming println! usage is wrong

5. Given these functions:

fn first() {
    println!("Start");
    second();
    println!("End");
}

fn second() {
    println!("Middle");
}

fn main() {
    first();
}

What is the order of printed lines when main runs?

hard

A. Start\nMiddle\nEnd

B. Middle\nStart\nEnd

C. Start\nEnd\nMiddle

D. End\nMiddle\nStart

Solution

1. Step 1: Trace the call flow from main

   Main calls first(), which prints "Start" then calls second().

2. Step 2: Follow nested function calls

   second() prints "Middle" and returns. Then first() prints "End".

3. Final Answer:

   Start\nMiddle\nEnd -> Option A

4. Quick Check:

   Call flow order = Start, Middle, End [OK]

Hint: Follow calls step-by-step to find print order [OK]

Common Mistakes:

• Ignoring nested function call order
• Assuming prints happen after all calls
• Mixing up print sequence