Output using println macro in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust code using println macro?

Consider the following Rust code snippet. What will it print when run?

Rust

fn main() {
    let x = 5;
    println!("The value of x is: {}", x);
}

A x = 5

B The value of x is: x

C The value of x is: {}

D The value of x is: 5

💡 Hint

Look at how the placeholder {} is replaced by the variable x.

The println! macro replaces {} with the value of x, which is 5, so it prints exactly: The value of x is: 5

❓ Predict Output

intermediate

What does this println macro print with multiple placeholders?

What is the output of this Rust code?

Rust

fn main() {
    let a = 3;
    let b = 7;
    println!("Sum of {} and {} is {}", a, b, a + b);
}

A Sum of a and b is a + b

B Sum of 3 and 7 is 10

C Sum of {} and {} is {}

D Sum of 3 and 7 is a + b

💡 Hint

Each {} is replaced by the corresponding argument in order.

The placeholders {} are replaced by a, b, and a+b respectively, so the output is: Sum of 3 and 7 is 10

❓ Predict Output

advanced

What is the output of this Rust code with named arguments in println?

Look at this Rust code using named arguments in println! macro. What will it print?

Rust

fn main() {
    let name = "Alice";
    let age = 30;
    println!("Name: {person}, Age: {years}", person=name, years=age);
}

A Name: {person}, Age: {years}

B Name: name, Age: age

C Name: Alice, Age: 30

D Name: Alice Age: 30

💡 Hint

Named arguments replace placeholders with matching names.

The placeholders {person} and {years} are replaced by the values of name and age variables, so it prints: Name: Alice, Age: 30

❓ Predict Output

advanced

What error does this Rust code produce when using println macro incorrectly?

What error will this Rust code produce?

Rust

fn main() {
    let x = 10;
    println!("Value is: {}", );
}

A error: expected expression, found `)`

B Value is: 10

C Value is: {}

D error: mismatched types

💡 Hint

Check if all placeholders have matching arguments.

The println! macro expects an argument for the {} placeholder, but none is provided, causing a syntax error: expected expression, found `)`

🧠 Conceptual

expert

How many items are printed by this Rust code using println! in a loop?

How many lines will this Rust program print?

Rust

fn main() {
    for i in 1..=5 {
        println!("Number: {}", i);
    }
}

A 5

B 4

C 6

D 1

💡 Hint

The range 1..=5 includes numbers from 1 to 5 inclusive.

The loop runs from 1 to 5 inclusive, so it prints 5 lines, one for each number.