Your First Rust Program

The main Function

Every executable Rust program must have a function named main. This is the entry point: when you run the compiled program, execution starts at the first line inside main and proceeds top to bottom.

Example: The main Function

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

Printing with println!

println! is a macro, not a regular function -- that is why it ends with an exclamation mark. It prints its argument to standard output followed by a newline character, making it the most common way to see output from a Rust program.

Note: Macros like println! can accept a variable number of arguments, which regular Rust functions cannot do.

Example: Printing with println!

fn main() {
    println!("This line has a newline after it");
    println!("So this prints on a new line");
}

Compiling and Running

You turn Rust source code into a runnable program with the rustc compiler, which produces a native executable. You then run that executable directly from the command line.

Example: Compiling and Running

rustc main.rs
./main

Statements End With Semicolons

Most lines of code inside a Rust function are statements, and Rust requires each one to end with a semicolon. Forgetting a semicolon is one of the most common early compiler errors.

Example: Statements End With Semicolons

fn main() {
    let message = "Semicolons separate statements";
    println!("{}", message);
}