Output using println macro in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, world!" using println! macro.

Rust

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

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

Aprintln

Bprint

Cformat

Deprintln

Attempts:

3 left

💡 Hint

Common Mistakes

Using print! instead of println! which does not add a new line.

Using format! which returns a string but does not print.

The println! macro prints text followed by a new line.

2fill in blank

medium

Complete the code to print the value of variable x using println! macro.

Rust

fn main() {
    let x = 5;
    println!("Value is: [1]", x);
}

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

A"x"

B"%d"

C"{x}"

D"{}"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around variable name inside the string.

Using C-style format specifiers like %d which are not valid in Rust.

The placeholder {} is used to print variable values in println!.

3fill in blank

hard

Fix the error in the code to correctly print the sum of a and b.

Rust

fn main() {
    let a = 3;
    let b = 4;
    println!("Sum is: [1]", a + b);
}

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

A"{a + b}"

B"a + b"

C"{}"

D"sum"

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the expression inside quotes so it prints literally.

Using variable names inside braces without formatting.

The placeholder {} is needed to print the result of a + b.

4fill in blank

hard

Fill both blanks to print the name and age variables using println! macro.

Rust

fn main() {
    let name = "Alice";
    let age = 30;
    println!("Name: [1], Age: [2]", name, age);
}

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

A"{}"

B"{name}"

D"{age}"

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names inside the string placeholders instead of {}.

Using only one placeholder for two variables.

Use {} placeholders for each variable in the string.

5fill in blank

hard

Fill all three blanks to print the uppercase name, age, and a greeting message.

Rust

fn main() {
    let name = "Bob";
    let age = 25;
    println!("[1] is [2] years old. [3]!", name.to_uppercase(), age, "Hello");
}

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

A"{}"

D"{name}"

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names inside the string placeholders instead of {}.

Mismatching the number of placeholders and arguments.

Use {} placeholders for each value. The first placeholder is for the uppercase name, so {name} is incorrect inside the string, but the argument name.to_uppercase() is passed.

Practice

1. What does the println! macro do in Rust?

easy

A. Creates a new variable

B. Prints text or values to the screen with a new line

C. Reads input from the user

D. Stops the program execution

Solution

1. Step 1: Understand the purpose of println!

   The println! macro is used to show messages or values on the screen, adding a new line after printing.

2. Step 2: Compare with other options

   Reading input, creating variables, or stopping the program are not tasks of println!.

3. Final Answer:

   Prints text or values to the screen with a new line -> Option B

4. Quick Check:

   println! prints output [OK]

Hint: Remember: println! always prints with a new line [OK]

Common Mistakes:

• Confusing println! with input functions
• Thinking println! creates variables
• Assuming println! stops the program

2. Which of the following is the correct syntax to print the number 5 using println! in Rust?

easy

A. println!("{}", 5);

B. println!(5);

C. println!("number: 5");

D. println!("5");

Solution

1. Step 1: Understand how to print values with placeholders

   To print a number using println! with a placeholder, use {} inside the string and pass the value after the comma.

2. Step 2: Check each option

   println!("5"); prints the string "5" literally, println!(5); is invalid syntax, println!("number: 5"); prints a fixed string without using a placeholder. println!("{}", 5); correctly uses {} to print the number 5.

3. Final Answer:

   println!("{}", 5); -> Option A

4. Quick Check:

   Use curly braces {} for values [OK]

Hint: Use curly braces {} to insert values inside println! [OK]

Common Mistakes:

• Trying to print numbers without quotes or placeholders
• Forgetting the comma between string and value
• Using invalid syntax without quotes

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

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

medium

A. Value: 10

B. Value: x

C. Value: {}

D. 10

Solution

1. Step 1: Identify the variable and placeholder

   The variable x holds the value 10. The println! uses {} to insert the value of x.

2. Step 2: Understand the output format

   The output will replace {} with 10, printing "Value: 10" exactly.

3. Final Answer:

   Value: 10 -> Option A

4. Quick Check:

   Placeholder {} shows variable value [OK]

Hint: Curly braces {} show variable values in output [OK]

Common Mistakes:

• Printing the variable name instead of its value
• Printing the placeholder literally
• Omitting the variable in println!

4. Identify the error in this Rust code:

let name = "Alice";
println!("Hello, name!");

medium

A. String quotes are incorrect

B. Variable name is not declared

C. println! macro is misspelled

D. Missing curly braces to print variable value

Solution

1. Step 1: Check how the variable is used in println!

   The code prints the string "Hello, name!" literally because it lacks curly braces to insert the variable name.

2. Step 2: Identify the fix

   To print the value of name, use {} inside the string and pass name after the comma.

3. Final Answer:

   Missing curly braces to print variable value -> Option D

4. Quick Check:

   Use {} to insert variables in println! [OK]

Hint: Use {} and comma to print variables, not plain text [OK]

Common Mistakes:

• Forgetting curly braces around variable
• Not passing variable after the string
• Assuming variable prints without placeholders

5. You want to print the message: "Temperature is 23°C" using println!. Which code correctly prints this message including the degree symbol?

hard

A. println!("Temperature is 23C");

B. println!("Temperature is 23\degree C");

C. println!("Temperature is 23\u{00B0}C");

D. println!("Temperature is 23\xB0C");

Solution

1. Step 1: Understand how to print special Unicode characters

   The degree symbol (°) can be printed using Unicode escape \u{00B0} in Rust strings.

2. Step 2: Check each option for correctness

   println!("Temperature is 23\u{00B0}C"); uses the correct Unicode escape. println!("Temperature is 23C"); does not include the degree symbol. println!("Temperature is 23\degree C"); uses an invalid escape. println!("Temperature is 23\xB0C"); uses a hex escape which is incorrect for Unicode in Rust strings.

3. Final Answer:

   println!("Temperature is 23\u{00B0}C"); -> Option C

4. Quick Check:

   Use \u{XXXX} for Unicode chars in Rust strings [OK]

Hint: Use \u{XXXX} for special Unicode characters in strings [OK]

Common Mistakes:

• Using invalid escape sequences
• Assuming special characters print without escapes
• Confusing hex and Unicode escapes