Compilation and execution flow in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, world!" in Rust.

Rust

fn main() {
    println!([1]);
}

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

AHello world

BHello, world!

C'Hello, world!'

D"Hello, world!"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the double quotes around the string.

Using single quotes instead of double quotes.

The println! macro requires a string literal inside double quotes to print text.

2fill in blank

medium

Complete the code to declare a variable named x with value 5.

Rust

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

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

Ax

Bvalue

Cnum

Dfive

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than the one printed.

Forgetting to declare the variable.

The variable name must match the one used in println!, which is x.

3fill in blank

hard

Fix the error in the code to correctly add two numbers and print the result.

Rust

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

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Using an invalid operator.

The plus sign (+) adds two numbers in Rust.

4fill in blank

hard

Fill both blanks to create a loop that prints numbers from 1 to 5.

Rust

fn main() {
    for i in [1] [2] 6 {
        println!("{}", i);
    }
}

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

A1..

B1..=

C6..

D..

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1..=6 which includes 6 and prints 6 as well.

Using 6..1 which is an invalid range.

The range 1..6 includes numbers from 1 up to but not including 6, which prints 1 to 5.

5fill in blank

hard

Fill all three blanks to create a function that returns the square of a number.

Rust

fn square([1]: i32) -> i32 {
    [2] * [3]
}

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

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

Anum

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inside the function.

Forgetting to return the multiplication result.

The function parameter and the multiplication both use the same variable name 'num' to calculate the square.

Practice

1. What is the first step when running a Rust program?

easy

A. Directly run the Rust source file without compiling

B. Compile the code using rustc to create an executable

C. Write the output to a file before compiling

D. Use an interpreter to execute the Rust code line by line

Solution

1. Step 1: Understand Rust's execution model

   Rust is a compiled language, so the source code must be compiled first.

2. Step 2: Identify the compilation tool

   The rustc compiler converts Rust code into an executable file.

3. Final Answer:

   Compile the code using rustc to create an executable -> Option B

4. Quick Check:

   Rust code is compiled first [OK]

Hint: Rust code must be compiled before running [OK]

Common Mistakes:

• Thinking Rust runs like a script without compiling
• Confusing Rust with interpreted languages
• Trying to run source code directly

2. Which command correctly compiles a Rust file named main.rs?

easy

A. run rustc main.rs

B. compile main.rs

C. rustc main.rs

D. cargo run main.rs

Solution

1. Step 1: Recall Rust compilation command

   The Rust compiler command is rustc followed by the filename.

2. Step 2: Check each option

   rustc main.rs matches the correct syntax: rustc main.rs.

3. Final Answer:

   rustc main.rs -> Option C

4. Quick Check:

   Use rustc filename.rs to compile [OK]

Hint: Use 'rustc' followed by filename to compile [OK]

Common Mistakes:

• Adding extra words like 'run' before rustc
• Using 'compile' instead of 'rustc'
• Confusing cargo commands with rustc

3. What will be the output when running this Rust program?

fn main() {
    println!("Hello, Rust!");
}

medium

A. Hello, Rust!

B. println!("Hello, Rust!");

C. Error: missing semicolon

D. No output

Solution

1. Step 1: Understand the println! macro

   This macro prints the string inside quotes to the console with a newline.

2. Step 2: Check the code correctness

   The code is syntactically correct and will print the message.

3. Final Answer:

   Hello, Rust! -> Option A

4. Quick Check:

   println! outputs the string [OK]

Hint: println! prints text to console with newline [OK]

Common Mistakes:

• Thinking println! prints the code itself
• Expecting no output without return statement
• Confusing macro syntax with function

4. Identify the error in this Rust code snippet:

fn main() {
    println!("Hello, world!")
}

medium

A. Missing closing parenthesis for println! macro

B. No error, code runs fine

C. Incorrect function name

D. Missing semicolon after println! macro

Solution

1. Step 1: Check statement termination syntax

   Rust requires semicolons to terminate expression statements like println! macro calls.

2. Step 2: Locate the missing semicolon

   The println! call is missing the terminating semicolon before the closing brace.

3. Final Answer:

   Missing semicolon after println! macro -> Option D

4. Quick Check:

   Expression statements require semicolon [OK]

Hint: Rust expression statements require a trailing semicolon [OK]

Common Mistakes:

• Thinking it's a parenthesis mismatch
• Confusing macros with block expressions
• Believing no semicolon needed before closing brace

5. You have two Rust files: lib.rs and main.rs. You want to compile main.rs which uses functions from lib.rs. What is the correct compilation and execution flow?

hard

A. Compile lib.rs into a library, then compile main.rs linking the library, then run the executable

B. Run main.rs directly without compiling lib.rs

C. Compile only main.rs, Rust automatically compiles lib.rs

D. Combine both files manually into one file before compiling

Solution

1. Step 1: Understand Rust's multi-file compilation

   The rustc compiler automatically handles referenced modules like lib.rs when compiling main.rs.

2. Step 2: Single command suffices

   With mod lib; in main.rs, rustc main.rs compiles both files and produces the executable.

3. Final Answer:

   Compile lib.rs into a library, then compile main.rs linking the library, then run the executable -> Option A

4. Quick Check:

   rustc main.rs compiles dependencies automatically [OK]

Hint: rustc compiles referenced modules automatically [OK]

Common Mistakes:

• Trying to run source files without compiling dependencies
• Assuming Rust compiles dependencies automatically at runtime
• Manually merging files instead of compiling separately