In this section, we will write our first Rust program: the classic "Hello, World!" This simple program will help you understand the basic structure of a Rust program and how to compile and run it.

1. Create a New Rust Project: Open your terminal and create a new Rust project using Cargo, Rust's package manager and build system.

   cargo new hello_world
   cd hello_world
   

   This command creates a new directory called hello_world with the following structure:

   hello_world
   ├── Cargo.toml
   └── src
       └── main.rs
   

2. Open the main.rs File: Navigate to the src directory and open the main.rs file in your favorite text editor. This file is where you will write your Rust code.

3. Write the Code: Replace the contents of main.rs with the following code:

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

   Explanation:

   • fn main() { ... }: This defines the main function, which is the entry point of every Rust program.
   • println!("Hello, world!");: This line prints the string "Hello, world!" to the console. The println! macro is used for printing text to the standard output.

1. Compile the Program: In your terminal, make sure you are in the hello_world directory and run:

   cargo build
   

   This command compiles your program and creates an executable file in the target/debug directory.

2. Run the Program: To run the compiled program, use the following command:

   cargo run
   

   You should see the following output:

   Hello, world!
   

Create a new Rust project and modify the main.rs file to print a custom message of your choice.

1. Create a new Rust project named custom_message.
2. Open the main.rs file in the src directory.
3. Replace the contents of main.rs with code that prints a custom message.
4. Compile and run the program to see your custom message.

1. Create the Project:

   cargo new custom_message
   cd custom_message
   

2. Modify main.rs:

   fn main() {
       println!("Welcome to Rust programming!");
   }
   

3. Compile and Run:

   cargo run
   

   Expected output:

   Welcome to Rust programming!
   

• Missing Semicolon: Ensure that each statement ends with a semicolon (;). For example, println!("Hello, world!") should be println!("Hello, world!");.
• Correct Syntax for println!: The println! macro requires an exclamation mark (!). Forgetting this will result in a compilation error.
• File Structure: Make sure you are in the correct directory when running cargo build or cargo run. These commands should be executed in the root directory of your project (e.g., hello_world).

In this section, you learned how to write, compile, and run a simple Rust program. You also learned about the basic structure of a Rust program and how to use the println! macro to print text to the console. This foundational knowledge will be essential as you progress through more complex Rust programs. Next, we will dive into Rust's basic syntax and structure to build on what you've learned here.