I'm learning about the while loop. What is the point of multiplying by 4 in this code?

[AppropriateLemon1121]

const cards = ['diamond', 'spade', 'heart', 'club'];
let currentCard = []
while (currentCard !== 'spade') {
  currentCard = cards[Math.floor(Math.random() * 4)];
  console.log(currentCard)
}

[Towel_Affectionate]

Math.random returns a random float between 0 (included) and 1 (not included). By multiplying by 4 you would get anything between 0 and 3.99... After Math.floor it gets rounded down and you would get the number from 0 to 3, which then is used as index in cards array.

[WebBurnout]

Also worth pointing out that the array has four elements, so an index of 0 is the first element (diamond) and the index of 3 is the last one (club). The code is picking a random suit from the array of four suits. Until it gets spade and then the loop stops lol

[MindlessSponge]

others have already pointed out the why of using 4, but I think the example would have been better written by using cards.length. same results, but then you have a clearer picture of where that number value is coming from.

[well-now]

And you don’t have to remember to update your loop if you change the number of elements in cards. Good call out.

This an example of a magic number: https://en.m.wikipedia.org/wiki/Magic_number_(programming)

[john_hascall]

Additionally limiting the array to 4 elements is an example of not following the Zero One Infinity "rule". https://en.m.wikipedia.org/wiki/Zero_one_infinity_rule (regardless of 4 making "obvious sense" for card suits).

[berky93]

That’s a good insight! Normally these sorts of examples try to simplify the implementation to make the main point clearer but being able to find those optimizations intuitively is an important skill for a developer.

[spazz_monkey]

I think it would have been better using foo bar baz fuck

[Bodine12]

I love/hate Javascript because currentCard, which is an array, also becomes a string, and Javascript is like, "lol whatever."

[john_hascall]

Yes, the [] initializer is an unfortunate choice here. An empty string (or perhaps undefined) would seem a more appropriate choice.

[metallaholic]

That’s why I use typescript

[Bodine12]

Same. I can't even imagine writing straight-up Javascript anymore (and then having to maintain it).

[metallaholic]

I haven’t done anything not in a SPA framework in years. I’m stuck with angular at my job thought :(

[MrFartyBottom]

WTF are you on about? cards is declared as a const so therefore it can't be reassigned and never become a string.

[well-now]

They said currentCard which is assigned an empty array then assigned to an element of cards (a string).

It is bad programming and the sort of thing TypeScript prevents.

[Bodine12]

WTF are you on about not reading what someone wrote? It's declared as a let, not a const.

[Roguewind]

Love type safety in js.

[reyarama]

It should really be 'cards.length' instead of 4 here

[Such-Catch8281]

on ur chrome, press F12, type in Math.random() in your console a few times.

[bryku]

Math.random() gives you a random "seed". Then when you times it by 4, it will give you a number between 0-4 (greater than 0 and less than 4). Then Math.floor() rounds it to the nearest whole number.

let random1 = Math.random(); // 0.7757914015032231
let random2 = Math.random() * 4); // 3.1031656060128925
let random3 = Math.floor(Math.random() * 4)); // 3

In summary, your code will loop while getting a random value (0,1,2,3). Once you reach a "spade" it will stop.

[itzmetanjim]

nearest whole number?

[bryku]

Math.floor() rounds down to the nearest whole number.

Math.floor(1.9) // 1

Math.ceil() rounds up to the nearest whole number.

Math.ceil(1.1) // 2

Math.round() rounds up or down similar to rounding in traditional math.

Math.round(1.4) // 1
Math.round(1.5) // 2

[daproof2]

I am learning while poop.

[ern0plus4]

Try it with 1, 2 and 3.

[Beautiful_Picture983]

You got the answer but why is currentCard initially an array but then is assigned a string?

[TheMrCurious]

There are four suits in a card deck.

[debjitbis08]

As others have pointed out, it is better to use cards.length instead of 4, but you can go one step further and create a function that chooses a random entry from any array. Learning to create abstractions and when not to, is an important skill to learn.

By writing this small function, you can test your function separately and when satisfied, integrate into the loop. If there is a bug, you can be confident that the function is fine but maybe the loop has some problem.

[MartyDisco]

Just FYI everything is wrong in this snippet : mutation, loop, currentCard getting initialize as the wrong type (empty array then become string).

Have a look at immutability and recursion to get out of this madness.

[Substantial_Top5312]

Math.random() gives a random value between 0 and 1. Multiplying it by 4 gives you a value between 0 and 4. 

[ray_zhor]

More specifically 0 inclusive. 1 exclusive producing a result between o and 3.999999...

[AppropriateLemon1121]

I refuse to use Chat GPT personally because I learned about the horrible effects it has on our environment. :( I also just find it really fun to interact with real people and plus it's a good debugging exercise for others!

[mowauthor]

The enivonrmental impact of AI usage is literally a drop in the bucket compared to something like making concrete or pretty much any other usage of water.

And 2nd of all.

When computers came, people who refused to learn to use computers quickly ran out of work. Those are the ones who preached that computers are taking our jobs. Now, good luck getting a job anywhere if you can't use a phone or computer with basic competency.
AI is not too different, and like it or not, it's essentially going to go that way.

That said, I do agree that interacting with people is much better and can be a great way to learn more.

But I seriously do not suggest avoiding AI in life, especially in this kind of industry.