How to structure a project with multiple files

Structure a multi-file Rust project by creating a src directory with a main.rs entry point and additional .rs files for modules, then declare them in main.rs using the mod keyword.

// src/main.rs
mod calculator;

fn main() {
    println!("Result: {}", calculator::add(2, 3));
}

// src/calculator.rs
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

1. Create the project directory and initialize it with Cargo. cargo new my_project && cd my_project

2. Create the src directory if it doesn't exist and add your module file. mkdir -p src && touch src/calculator.rs

3. Declare the module in src/main.rs using the mod keyword. mod calculator;

4. Import and use the public items from the module in main.rs. use calculator::add;

5. Build and run the project to verify the structure works. cargo run

Think of your project like a book where main.rs is the cover and introduction, and other files are chapters containing specific details. You use the mod keyword to tell the main file where to find these chapters. This keeps your code organized so you don't have to read a single massive file to understand how your program works.