Chapter 1 - Hello, World!

Notes regarding the book

In many portions of the book, you may see statements like:

#![allow(unused)]
fn main() {
let ignore = 0;
}

It usually implies that the statment is inside a function (like fn main()) and you can simply click the unhide button that appears when you hover over the code snippet

Hello world is the first program that most programming languages teach beginners. Many tutorials will teach you how to “print” Hello, World! to the terminal / console as the first project

In rust, everything starts with a main function (annotated with fn).

Ignore what a function is for now. Just imagine a function as a container with things inside it. We will cover functions more in Chapter 4

This main function is the entry point of the program.

If you run the program, the main function will be executed.

You can use cargo to create a new project (cargo new project_name) and the below code will be preset in src/main.rs.

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

Rust also has it’s unique macros which are somewhat similar to functions, so you can ignore them for now.

As of now, I do not plan on covering macros in this book so you might want to check out the official book after this book to find out more about macros.

Comments

Comments are used to explain the code. The compiler does not care about comments.

// means the rest of the line from this point on is a comment

/* and */ means everything between is to be ignored / is a comment

You can see how comments are written inside code in this example:

// This is a single line comment
/* This is a multi-line comment
   It can span multiple lines */
fn main() {
    println!(/*This comment gets ignored by the compiler*/"Hello, World");
    // The above line is equivalent to the below line to the compiler
    println!("Hello, World");
}

The rust community rarely uses multiline comments and usually resorts to single line comments more. This is because they are an idiomatic comment style. So please support the idiots by using inline comments.