Arithmetic Operators

Goal of This Episode

Learn to add, subtract, multiply, divide, and take remainders in Rust.

Main Text

Today we’re doing math! Don’t worry — it’s just arithmetic.

The Four Basic Operations

First, create two variables:

fn main() {
    let a = 10;
    let b = 3;

    println!("{} + {} = {}", a, b, a + b); // 13
    println!("{} - {} = {}", a, b, a - b); // 7
    println!("{} * {} = {}", a, b, a * b); // 30
    println!("{} / {} = {}", a, b, a / b); // 3
    println!("{} % {} = {}", a, b, a % b); // 1
}

Wait — How Is 10 / 3 Equal to 3?

Good question! Because a and b are both integers, Rust performs integer division: everything after the decimal point simply gets chopped off. 10 divided by 3 is 3.333…, and chopping off the decimals gives 3.

What Is %?

% is the remainder operator (the modulo operation). 10 divided by 3 is 3 with a remainder of 1, so 10 % 3 is 1.

You can think of it as: “How many 3s fit inside 10? Three of them, with 1 left over.” That leftover is the remainder.

Using Multiple {}s

Did you notice? We put three {}s inside println!:

fn main() {
    let a = 10;
    let b = 3;
    println!("{} + {} = {}", a, b, a + b);
}

Rust fills in the values in order:

• The first {} → the value of a (10).
• The second {} → the value of b (3).
• The third {} → the value of a + b (13).

The number of {}s matches the number of values that follow, and the order must line up.

Recap

• The five arithmetic operators: + (addition), - (subtraction), * (multiplication), / (division), % (remainder).
• Integer division discards the decimal part (10 / 3 is 3, not 3.333).
• % takes the remainder: 10 % 3 is the 1 left over after dividing 10 by 3.
• println! can contain multiple {}s, matched in order with the values that follow.