freeCodeCamp/guide/english/rust/hello-world/index.md

title
Hello World

Hello Rust

Writing your first Rust program is as easy as installing it. In the project directory of your choice, create a new source file called main.rs. It is important to note that Rust files always end with the .rs extension and filenames with more than one word are separated with underscores. For example, helloworld.rs would become hello_world.rs.

After creating main.rs, add the following code within:

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

Wow! That was easy, wasn't it? Within you're new main.rs file, the following is true:

• The first line fn main() denotes a function in Rust. The main function is special, it is the first thing that is called for every executable Rust program.
• The second line println!("Hello, world!") is calling a Rust macro, passing a string as it's first argument. This line prints the string "Hello, world!" to the terminal. You can tell if you are calling a Rust macro or function through observation of the !.

To execute the program, you must first compile it:

$ rustc main.rs

This process will create an executable in the same directory, which you can then run:

$ ./main
Hello, world!

Congratulations! You've just written your own Rust program!

Hello Cargo

Cargo is the build tool that gets shipped with Rust when you installed it and can be used for many things. Here we will see the alternative approach of using cargo.

Firstly navigate to the parent directory of your project and run cargo new hello_world. This will create our project directory of hello_world with some files inside it, those being Cargo.toml which tells cargo how to build your project, as well as src/main.rs which is our Rust source file. If you open this file you will see some code is already generated for us to run hello world! So let's do that.

To run your program with cargo it is as simple as running cargo run in your project directory and it should look something like this:

cargo run
   Compiling hello_world v0.1.0
    Finished dev [unoptimized + debuginfo] target(s) in 1.31s
     Running `target/debug/hello_world`
Hello, world!

Great work you now have even more tools at your disposal!