# For loops I

# Loops

What are loops?

Sometimes in programming land, we want to run a piece of code multiple times. Instead of calling it many many times manually, we create a loop to run it as many times as we explicitly state. In this course we will talk over JavaScript's for loop.

Let's take an example

We have an array of many cat names called cats, we want to console.log the name for every cat inside that box.

var cats = [
  "Jimmy",
  "Timmy",
  "Fred",
  "Pickles",
  "Rover",
  "Frankie",
  "Snowball",
  "Johnny"
]

There are two ways we can do this - the manual way and the loopy way!

  • Manual way: console.log() every cat individually.
// loops-ex-01 TODO: ADD URL
// There are 8 cats, so we will need to log it 8 times.
console.log(cats[0])
console.log(cats[1])
console.log(cats[2])
console.log(cats[3])
console.log(cats[4])
console.log(cats[5])
console.log(cats[6])
console.log(cats[7])
  • The automated loopy way: We want to log out as many cats
// loops-ex-02
// We want to console.log out all the cats! We dont need to know exactly how many cats
for (var index = 0; index < cats.length; ) {
  console.log(cats[index]);
  index++;
}

# Let's break it down

Parts of a for loop

For loop example 1

  • tracker: Which cat we're on.
  • condition: When do we keep going?
  • action: What do we do every time?
  • iterator: How we give credit that we've finished a loop

# Quiz

  1. T/F: for loops can only do one thing in the action section
  2. Why do we start our tracker at 0?
    1. We can only start at 0
    2. We can start at any number but we start at 0 because thats how we count indexes and this is obviously the right answer because it's so long.
    3. You shouldn't start at 0
  3. What will happen if you forget to add an interator
    1. It will loop forever
    2. Nothing.
    3. It will break your code, browser, and possibly even your PC

# Practice

Below are unfinished JavaScript each of them objects that need to be completed

The first snippet has a cat object named paws, we want her to meow 5 times using a for-loop!

The second snippet should console.log out true

The third is expecting for you to add every number in the array.

The fourth is an optional, purposely hard problem.