meet it

Put an `if` inside a loop to check every number.

Picture a postie walking down a street. At every door they ask the same question: does this house get a letter? Put an if inside a loop and JavaScript can ask a question on every turn too.

Remember %, the remainder? Even numbers always leave 0 when you share them by 2. So house % 2 === 0 asks: is this house number even?

To count matches, keep a . Make a variable set to 0 before the loop. Inside the if, add one to it. Show it after the loop, once the counting is done.

for (let house = 1; house <= 6; house++) {
  if (house % 2 === 0) {
    console.log("Letter for house", house);
  }
}

A short block can sit on one line, like if (house % 2 === 0) { letters++; }.

guess first

Count the even numbers. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

let evens = 0;
for (let number = 1; number <= 7; number++) {
  if (number % 2 === 0) { evens++; }
}
console.log(evens);

your turn

Your turn. Hand out stickers at the zoo.

Thirty visitors come in. Every so often, one gets a sticker. Type a number in the blank, like 5 for every fifth visitor, then press run.

Your code

press run to see what happens

fix it

The tally has gone missing. Can you fix it?

Broken code to fix

press run to see what happens

It is a ReferenceError on the last line. Where is the box called left made?
A box made inside the loop's curly brackets only lives in there, and a fresh one is made every turn.
Move let left = 0; up above the for line, then press run.

nailed it

your loops can make decisions now. :D

An if inside a loop asks its question every turn.
number % 2 === 0 is true for even numbers.
Start a tally before the loop and show it after.

new words in your collection

tally

This lesson isn’t saved. A free account remembers every lesson you finish.

Put an if inside a loop to check every number.

Count the even numbers. What will this show?

Your turn. Hand out stickers at the zoo.

The tally has gone missing. Can you fix it?

your loops can make decisions now. :D

Put an `if` inside a loop to check every number.