Output using println macro in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the println! macro do in Rust?

It prints text to the console followed by a new line, allowing you to display output to the user.

beginner

How do you print a variable's value using println!?

Use curly braces {} as a placeholder inside the string, and pass the variable after the comma. Example: println!("Value: {}", x);

beginner

What happens if you use println! without any arguments?

It prints an empty line (just a new line) to the console.

intermediate

Can println! print multiple variables? How?

Yes, by using multiple placeholders {} and passing variables in order. Example: println!("{} and {}", a, b);

intermediate

What is the difference between print! and println! macros?

print! prints text without adding a new line at the end, while println! adds a new line after printing.

What will println!("Hello, {}!", "Rust"); output?

A Hello, Rust!

B Hello, {}!

C Hello, "Rust"!

D Error

The placeholder {} is replaced by the string "Rust", so it prints: Hello, Rust!

Which macro adds a new line after printing?

A print!

B println!

C write!

D format!

println! adds a new line after printing, unlike print!.

How do you print two variables a and b using println!?

A println!("{} {}", a, b);

B println!(a, b);

C println!("a and b");

D println!("{}", a + b);

Use placeholders for each variable and pass them in order.

What does println!(); print?

A Nothing

B A blank line

C Error

D The text 'println!'

It prints a blank line (just a new line).

Which of these is correct to print the value of variable x?

A println!("x");

B println!("{}", x);

C println!(x);

D println!("{x}");

Use {} as a placeholder and pass the variable after the comma.

Explain how to use the println! macro to print text and variables in Rust.

Think about how you combine text and values inside the macro.

What is the difference between print! and println! macros? When would you use each?

Consider how output appears on the console.

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