Operator Precedence

Goal of This Episode

Understand Rust’s order of operations — multiplication and division before addition and subtraction — and how to change the order with parentheses.

Main Text

Last episode we learned addition, subtraction, multiplication, and division — but what if we mix them together? Which one does the computer compute first?

Multiplication and Division First, Then Addition and Subtraction

fn main() {
    println!("{}", 2 + 3 * 4);
}

What do you think the answer is?

If you thought 20 (first 2 + 3 = 5, then times 4), that’s wrong!

The answer is 14. Just like in math, Rust does multiplication and division before addition and subtraction. So it first computes 3 * 4 = 12, then 2 + 12 = 14.

Changing the Order with Parentheses

What if you really do want the addition to happen first? Just add parentheses:

fn main() {
    println!("{}", (2 + 3) * 4);
}

This time the answer is 20. Whatever is inside the parentheses gets computed first: 2 + 3 = 5, then 5 * 4 = 20.

A Little Tip

When you’re not sure about the order, just add parentheses. Parentheses don’t just change the order — sometimes they also make code easier to read. Even when the order is already correct, there’s no harm in adding parentheses to make your intent clearer.

fn main() {
    // These two lines give the same result, but the second is clearer
    println!("{}", 2 + 3 * 4);
    println!("{}", 2 + (3 * 4));
}

Recap

• Rust’s operator precedence works just like math: multiplication and division come before addition and subtraction.
• Parentheses () force a different order of operations.
• When operator precedence isn’t obvious, parentheses can make the intended order clearer.