Arithmetic Operators

In the previous lesson, we learned how JavaScript converts between types. Now let’s start working with operators, beginning with arithmetic operators that do math.

➕ What are Arithmetic Operators?

Arithmetic operators perform math on numbers, just like you do on a calculator. They take two values and produce a result.

Here they are in code:

const price = 100;
const quantity = 3;

console.log(price + quantity); // 103
console.log(price - quantity); // 97
console.log(price * quantity); // 300
console.log(price / quantity); // 33.333...

Let’s walk through what each line does:

• We store 100 in price and 3 in quantity, so we have two numbers to work with.
• price + quantity adds them, giving 103.
• price - quantity subtracts quantity from price, giving 97.
• price * quantity multiplies them, giving 300.
• price / quantity divides price by quantity, giving a long decimal 33.333... because the numbers don’t divide evenly.

➗ The Remainder Operator

The remainder operator % gives you what is left over after division. It is very useful for checking if a number is even or odd.

console.log(10 % 2); // 0  → 10 divides evenly, so it is even
console.log(7 % 2); // 1  → 7 leaves a remainder, so it is odd

Let’s read each line:

• 10 % 2 divides 10 by 2 with nothing left over, so the remainder is 0. A remainder of 0 means the number is even.
• 7 % 2 divides 7 by 2 and leaves 1 behind, so the remainder is 1. A remainder that is not 0 means the number is odd.

🔼 Increment and Decrement

The ++ operator adds one to a number, and -- subtracts one. They are often used in loops to count.

let count = 5;

count++; // same as count = count + 1
console.log(count); // 6

count--; // same as count = count - 1
console.log(count); // 5

Let’s step through it:

• We start with count set to 5.
• count++ adds one to count, the same as writing count = count + 1, so count becomes 6.
• count-- subtracts one from count, the same as writing count = count - 1, so count goes back to 5.

🧮 Operator Precedence

When you combine operators, JavaScript follows the same order as math: multiplication and division happen before addition and subtraction. Use parentheses to control the order yourself.

console.log(2 + 3 * 4); // 14  → 3 * 4 happens first
console.log((2 + 3) * 4); // 20  → parentheses happen first

Let’s compare the two lines:

• In 2 + 3 * 4, JavaScript runs 3 * 4 first (getting 12), then adds 2, giving 14.
• In (2 + 3) * 4, the parentheses force 2 + 3 to run first (getting 5), then multiply by 4, giving 20.

⚠️ Common Mistakes to Avoid

🔧 Try It Yourself!

🧩 What You’ve Learned

• ✅ Arithmetic operators do math: +, -, *, /, %, and **
• ✅ The remainder operator % is useful for checking even or odd numbers
• ✅ ++ adds one and -- subtracts one
• ✅ Multiplication and division run before addition and subtraction
• ✅ Parentheses control the order of operations

🚀 What’s Next?

Now that you can do math, we will learn how to compare values. Let’s continue to Comparison Operators.