Main function

Let's look again at our first project source code:

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

It only contains a main function—this is where the execution of the program begins. It is a function that takes no arguments (hence the empty parentheses) and returns a unit, also written (). The body of the function, between curly brackets, contains a call to the println!() macro—we can see this is a macro because it ends with !, as opposed to a function. This macro prints the text between parentheses, followed by a new line. We'll see what is a macro in the Macros section.