Hello, Cargo

By the end of this part you’ll have a binary that runs. That’s it — no word counting yet. The point is to make the edit-build-run loop feel automatic before we add real logic.

What you need

• rustup — installs rustc, cargo, and keeps them updated
• Any editor. rust-analyzer is worth setting up early

Check your install:

cargo --version

Create the project

cargo new wordcount
cd wordcount

Cargo generates three things worth knowing:

Run it

cargo run

You should see Hello, world!. Cargo compiled a debug build into target/debug/ and executed it.

Make it yours

Open src/main.rs and replace it:

fn main() {
    let name = "wordcount";
    println!("{name} v{}", env!("CARGO_PKG_VERSION"));
}

Two things happened there:

• println! is a macro, not a function — the ! is how you tell. It formats at compile time, so a mismatched placeholder is a compile error, not a runtime surprise.
• env!("CARGO_PKG_VERSION") reads the version out of Cargo.toml during compilation.

Run it again:

cargo run
# wordcount v0.1.0

The loop you’ll use constantly

cargo check    # type-check only — fastest feedback
cargo run      # build + run
cargo build --release   # optimized build, much slower to compile

Reach for cargo check while you’re iterating. It skips code generation, so it’s often several times faster than a full build.

Before moving on

Try breaking it on purpose: change {name} to {nmae} and run cargo check. Read the error. Rust’s compiler messages are the best teaching tool in the language — get used to actually reading them instead of scanning for the line number.

Next up: reading arguments off the command line.