JavaScriptLesson 3 of 16

Numbers and operators

JavaScript counts like a calculator, only faster and with a couple of surprises. Let’s look at operators, remainders and rounding.

Key points

+ - * / are the usual maths, ** is a power: 2 ** 10 is 1024
% gives the remainder of a division: 7 % 3 is 1
Math.floor rounds down, Math.round rounds normally, Math.max picks the largest
0.1 + 0.2 gives 0.30000000000000004, so money is rounded with toFixed(2)
"5" + 2 glues text into "52", while Number("42") turns text into a number

Example

console.log(7 + 3, 7 - 3, 7 * 3, 7 / 2);console.log(7 % 3, 2 ** 10);console.log(0.1 + 0.2);console.log((0.1 + 0.2).toFixed(2));console.log(Math.round(4.6), Math.floor(4.6), Math.max(3, 9, 1));console.log("5" + 2, "5" * 2, Number("42") + 1);

The last line is a classic trap: with a plus, text wins and gets glued, while multiplying turns "5" into a number. toFixed returns a string with as many decimals as you ask for.

Task

How to use the editor⌘ Enter or Ctrl Enter runs the code, ⇧ ⌘ Enter checks the task.Tab and Shift Tab indent the line or the selection; Esc, then Tab leaves the editor.The check compares what the program printed with the task; spaces at line ends do not matter.After two failed checks you may open the solution. Your code is kept in this browser.

Seven friends share three pizzas of 12 slices, and a pizza costs 11.5. Print three lines: Slices each: 5 (whole slices per friend), Left over: 1 (what remains) and Each pays: 4.93 (each share, rounded to cents).

// Pizza night: 3 pizzas, 12 slices each, 7 friendsconst pizzas = 3;const slicesPerPizza = 12;const friends = 7;const pricePerPizza = 11.5; const totalSlices = pizzas * slicesPerPizza;// TODO: whole slices for each friend (Math.floor) and slices left over (%)// TODO: what each friend pays, rounded to cents with toFixed(2)// Print three lines:// Slices each: 5// Left over: 1// Each pays: 4.93

// Pizza night: 3 pizzas, 12 slices each, 7 friends
const pizzas = 3;
const slicesPerPizza = 12;
const friends = 7;
const pricePerPizza = 11.5;

const totalSlices = pizzas * slicesPerPizza;
// TODO: whole slices for each friend (Math.floor) and slices left over (%)
// TODO: what each friend pays, rounded to cents with toFixed(2)
// Print three lines:
// Slices each: 5
// Left over: 1
// Each pays: 4.93

Output

What your program prints appears here.