Control Flow

if expressions

  • The code inside an if block is called an arm, similar to match.

    fn main() {
    let number = 3;

    if number < 5 {
        println!("condition was true"); // An arm
    } else {
        println!("condition was false");
    }
}

  • You can only pass a bool to the if expression

    // FAIL: number is of type integer and not bool
fn main() {
    let number = 3;

    if number {
        println!("number was three");
    }
}

// This works since it's a condition
fn main() {
    let number = 3;

    if number != 0 {
        println!("number was something other than zero");
    }
}

  • Rust only executes the block for the first true condition, and once it finds one, it doesn't even check the rest:

    fn main() {
    let number = 6;

    if number % 4 == 0 {
        println!("number is divisible by 4");
    } else if number % 3 == 0 {
        println!("number is divisible by 3"); // Only this statement will run
    } else if number % 2 == 0 {
        println!("number is divisible by 2");
    } else {
        println!("number is not divisible by 4, 3, or 2");
    }
}

  • Conditionals in Single Line:

    // This Works
fn main() {
    let condition = true;
    let number = if condition { 5 } else { 6 };

    println!("The value of number is: {}", number);
}

// FAIL: Different data types integer and string
fn main() {
  let condition = true;

  let number = if condition { 5 } else { "six" };

  println!("The value of number is: {}", number);
}