1. Hello World

Introduction to Cargo

First, I am deeply into the C language. In my opinion, rewrite and conquer is a stupid way, as the C language has improved in a few decades. As a result, I am learning Rust as a whole different language.

Also, I don't have any interest in rewriting something in Rust (some call it RIIR).

Cargo: The Modern App Creator

Rust uses cargo to create Rust apps.

Simply run this:

cargo run hello_world

Directory Structure

yjlee@yjlee-linuxonmac:~/learn-rust/hello_rust$ tree
.
├── Cargo.toml
└── src
└── main.rs

2 directories, 2 files
yjlee@yjlee-linuxonmac:~/learn-rust/hello_rust$

The project file is called Cargo.toml.

Let's read this post.

[package]
name = "hello_rust"
version = "0.1.0"
edition = "2024"

[dependencies]

Rust has various editions, like Rust 2021 and Rust 2024. Many Rust communities recommend Rust 2024, as it supports more syntactic sugar. And people say that it is safer, but I am not sure why programming languages always try to do everything instead of programmers.

I am pretty sure I would compare C23 and Rust 2024 in my posts, but please consider I have a strong perspective based on C17/C23 conventions.

Main Function

The main function is still simple.

When you run main.rs, there are a few keywords that are notable.

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

Keyword	Meaning
fn	Function
main	Entrypoint
println	Macro Name
!	Macro Func
{	Open Brace
}	Close Brace
""	Literal Type
()	Retrieves Args
;	Semicolon

Build

cargo build

or directly run:

cargo run

Run

The default build is a debug build. Run this:

Unix / Linux

./target/debug/hello_rust

Windows

.\target\debug\hello_rust

Scope

Rust has a scope. And when a variable is asserted within a scope, you cannot* use it outside.

A scope is separated by {} braces.

fn main() {
  // Let's call it "Scope 1"
  {
    let str1 = String::from("Hello, world!");
    println!("{}", str1);
    // str1 can be used in this scope
  }
  println!("{}", str1); // No parasan! You can't go inside.
}

You cannot compile this as you tried to use str1 outside of Scope 1.

This is also similar when you use Modern C++. It is definitely safe, but I'm still not sure if a programming language must do these things without a programmer's permission.

Next Steps?

• Int Types
• Float Types

Then...

• String Types
• If-Else If-Else