Output using println macro in Rust

Introduction

We use the println! macro to show messages or results on the screen. It helps us see what our program is doing.

To display a greeting message to the user.

To show the result of a calculation.

To print debugging information while writing code.

To output instructions or prompts during a program.

To confirm that a program step has completed.

Syntax

Rust

println!("text to show");
println!("Hello, {}!", name);

The println! macro prints text and adds a new line at the end.

You can insert values inside the text using curly braces {} and provide the values after the comma.

Examples

Prints a simple message.

Rust

println!("Hello, world!");

Prints a message with a number inserted.

Rust

let age = 25;
println!("I am {} years old.", age);

Prints a message with a name inserted.

Rust

let name = "Alice";
println!("Welcome, {}!", name);

Sample Program

This program prints a greeting with a name, shows a score, and then prints a congratulation message.

Rust

fn main() {
    let name = "Bob";
    let score = 42;
    println!("Hello, {}!", name);
    println!("Your score is {}.", score);
    println!("Good job!");
}

Important Notes

Remember to use the exclamation mark ! after println because it is a macro, not a function.

Each println! adds a new line automatically, so you don't need to add \n inside the string unless you want extra lines.

Summary

println! is used to print text and values to the screen with a new line.

You can insert values inside the text using curly braces {}.

It helps you communicate with the user or check what your program is doing.

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