Functions

Rust code uses snake case as the conventional style for function and variable names. In snake case, all letters are lowercase and underscores separate words.

If we define another_function after the main function, it doesn't matter. We could have defined it before as well. Rust doesn’t care where you define your functions, only that they’re defined somewhere.

Pass parameters

fn main() {
    another_function(5, 6);
}

fn another_function(x: i32, y: i32) {
    println!("The value of x is: {}", x);
    println!("The value of y is: {}", y);
}

Function Bodies Contain Statements and Expressions

Statements are instructions that perform some action and do not return a value. Expressions evaluate to a resulting value.

fn main() {
    let y = 6;
}

• function definitions are statements.

• let y = 6; is statement.

• Statement do not return values => can't assign let statement to another value

  ex) let x = (let y = 6); // x

  In Rust, such an expression "x = y = 6;" can't happen.

• Expressions can be part of statements.

  fn main() {
    let x = 5;
    let y = {
      let x = 3;
      x + 1 // **do not include semicolon**
    }
    println!("y : {}", y); // y : 4
  }
  

  • Expressions do not include ending semicolons.

    -> If I put semicolon, then it doesn't return. It becomes statement.

    fn main() {
        let x = plus_one(5);
    
        println!("The value of x is: {}", x);
    }
    
    fn plus_one(x: i32) -> i32 {
        x + 1  // ** don't put semicolon
          // semicolon을 붙이면 나는 에러 : type 이 맞지 않는다는 것 : found type ()
    }