Lesson 3

Numbers in JavaScript

+ addition operator, e.g. 2 + 2 = 4
- subtraction operator, e.g. 10 - 6 = 4
* multiplication operator, e.g. 5 * 6 = 30
/ division operator, e.g. 8 / 4 = 2
% modulo operator, returns the remainder after dividing one number by another, e.g. 10 % 7 = 3

Some functions
Math.round() rounds a number to the nearest whole number, e.g. Math.round(7.8567) = 8
Math.floor() rounds a number DOWN to the nearest whole number, e.g. Math.floor(17 / 5) = 3
Math.ceil() rounds a number UP to the nearest whole number, e.g. Math.ceil(7.1) = 8
Math.random() returns a random decimal number between 0 (included) and 1 (excluded), e.g. Math.random() = 0.732...
Math.abs() returns the absolute value of a number, e.g. Math.abs(-5) = 5
Math.min() used to find the smallest of the given numbers, e.g. Math.min(4, 9, 2) = 2
Math.max() used to find the largest of the given numbers, e.g. Math.max(4, 9, 2) = 9
Number() used to convert a given value (like a string) into a number, e.g. Number("5") = 5
parseInt() converts a string into a whole number, e.g. parseInt("5") = 5

Store a Number

Task: Store your own age in a variable and print it.

let age = 10;
console.log(age);

Basic Math

Task: Pick two numbers of your own and try all four operations.

let a = 8;
let b = 3;
console.log(a + b);
console.log(a - b);
console.log(a * b);
console.log(a / b);

The Remainder Operator (%)

Task: Try % with a few number pairs and guess the pattern before running it.

console.log(10 % 3);

Numbers + Strings Together

Task: Predict the output of each line before running it, then compare.
Why they are different (string vs number)?

console.log("5" + 3);
console.log(5 + 3);

Age in 10 Years

Task: Calculate your age in 10 years and print a sentence using a template literal.

let age = 10;
let futureAge = age + 10;
console.log(`In 10 years I will be ${futureAge}.`);

Rounding Numbers

Task: Try Math.round() on a few decimal numbers and see how it rounds.

let price = 7.8567;
console.log(Math.round(price));

Random Numbers

Task: Run it several times and see the dice value change.
Why do we add +1 at the end?

let dice = Math.floor(Math.random() * 6) + 1;
console.log(dice);

Pizza Slice Splitter

Task: Change the numbers of slices/friends and recalculate.
What does Math.floor do here, and why do we need it?

let slices = 17;
let friends = 5;

let slicesEach = Math.floor(slices / friends);
let leftover = slices % friends;

console.log(`Each friend gets ${slicesEach} slices.`);
console.log(`There are ${leftover} slices left over.`);

Temperature Converter

Task: Convert 3 different Celsius temperatures (like todays weather, freezing point 0°C, and body temp 37°C) to Fahrenheit.

let celsius = 25;
let fahrenheit = (celsius * 9 / 5) + 32;
console.log(`${celsius}°C is ${fahrenheit}°F`);

Allowance Growth Challenge

Task: Manually calculate savings after 8 weeks by repeating the line.

let savings = 5;
savings = savings + 5; // week 2
savings = savings + 5; // week 3
savings = savings + 5; // week 4
console.log(`After 4 weeks I will have $${savings}`);

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