Blackjack program in javascript

shivajikobardan · Jun 21, 2023

JavaScript:

let card_value = 0;
let count_of_a = 0;
let number_of_cards = Number(prompt("Enter the number of cards."));
if (number_of_cards >= 2 && number_of_cards <= 5) {

  let cards = [];
  for (let i = 0; i < number_of_cards; i++) {
    cards[i] = prompt("Enter the value of card ");
  }
  var dict = {

    "2": 2,
    "3": 3,
    "4": 4,
    "5": 5,
    "6": 6,
    "7": 7,
    "8": 8,
    "9": 9,
    "t": 10,
    "j": 11,
    "q": 12,
    "k": 13
  };

  for (let j of cards) {
    if (j == "a") {
      count_of_a++;
      continue;
    }
    else {
      card_value += dict[j];
    }
  }
  for (let k = 0; k < count_of_a; k++) {
    dict["a"] = (card_value + 11 > 21) ? 1 : 11,
      card_value += dict["a"];
  }
  console.log(card_value);
}
else {
  console.log("Program ends here. Please enter again.");
}

Is my code correct?

.Scott · Jun 21, 2023

I believe the face cards (j,q,k) are suppose to score ten each. Not 11, 12, 13.

DrClaude · Jun 22, 2023

Your algorithm may not work properly when there are more than one ace, for instance "T A A".

pbuk · Jun 22, 2023

shivajikobardan said:

Is my code correct?

The best way to find this out is to test it. Real programmers use a unit test framework (for JavaScript we have mocha, Jest or AVA) but for now I would use something like this:

JavaScript:

function runTests(subject, tests) {
  for (const [description, input, expected] in tests) {
    const actual = subject(input);
    if (actual === expected) {
      console.log(description, 'passed');
      continue;
    }
    console.log(description, 'failed', { expected, actual });
  }
}

runTests(calculateScore, [
  ['It should calculate Ace high', [5, 5, 'a'], 21],
  ['It should calculate Ace low', [5, 6, 'a'], 12],
  ...
]);

First you need to separate the calculation part from the parts accepting input and reporting results: this is called separation of concerns and is a vital concept in any programming language.

pbuk · Jun 22, 2023

@.Scott @DrClaude net vs. fish: serial hungry man here.

.Scott · Jun 22, 2023

pbuk said:

@.Scott @DrClaude net vs. fish: serial hungry man here.

Beginner programmers need mentorship. Apparently, PF is what he has.

shivajikobardan · Jun 22, 2023

pbuk said:

First you need to separate the calculation part from the parts accepting input and reporting results: this is called separation of concerns and is a vital concept in any programming language.

Hey, so my code is working right? except the fact j,k,q are 10? How do you separate calculation parts from accepting input part?

.Scott · Jun 22, 2023

shivajikobardan said:

How do you separate calculation parts from accepting input part?

First let me make sure you understand why you would separate it - which is to assist in unit testing. If you put lines 10 to 38 of your JavaScript code into a function (I'll call it Score21), then you can write test code that passes is test cases and checks the result for accuracy (a @pbuk suggested). Lines 10 to 38 are the meat of your code - where subtle errors are most likely. So if you can systematically run a dozen well-chosen test cases against it, it can provide your and others with confidence-inspiring evidence that the code is doing what you want.

Of course, that still leaves your other 15 lines of code untested. Testing those require feeding the "prompt" function and checking the output of the console.log function. There are techniques for doing that automatically, but let's leave it as just a manual test procedure - run the program, enter test values, read and verify the result.

There is a part 2 to this. Two months later, the requirements change a bit. Say you want to support '0' and an alternate to 't' for specifying the "ten" card. So you make the appropriate changes, and then rerun the original test for function Score21. That would be a "regression test" and it tells you whether you have broken anything.

Then you would update that regression test to include another 1 or 2 test cases for the new "0" feature and test it again.

Then repeat the manual testing.
Finally put together the design/test-report/code merge request package for peer review - but that's a whole new topic.

Mark44 · Jun 22, 2023

.Scott said:

I believe the face cards (j,q,k) are suppose to score ten each. Not 11, 12, 13.

And this is stated in the problem description.

RayDonaldPratt · Jan 24, 2024

As I understand your code, you will choose the total number of cards, between 2 to 5 cards, without predetermining the value of each card, and then you will iterate through each of your chosen total number of cards and assign each card its value in an array (cards[]).

You will then iterate through your cards[] array and add the total of each card to the card_value variable (card_value += dict[j];), but aces ("a") are not yet in the dictionary object, so if your code encounters an ace ("a"), it will simply count the number of aces without yet adding any number to the card-value variable:
if (j == "a") {
count_of_a++;
* * *
}

After counting the number of aces, your program will ask that number of times if the card_value total of all the cards plus 11 is less than 21. If less than 21, your program will assign the value of 11 to "a" in your dictionary object and add that value to the card_value total of all the cards, but if the total card_value plus 11 is equal to or greater than 21, then your program will assign the value of 1 to your dictionary object and add that value to the card_value total of all the cards. Thus, the value of "a" in your dictionary object can change.

Barring any syntax issues, it is a clever piece of logic.

Finally, your program writes your hand total to console.log, though it does not display whether the hand busted as you originally intended.

I put your program into the Code IDE, and all the brackets seem to be correctly nested. I would put the program as javascript inside an html page with some different coding to display everything to see if it works, but I have not done so.

Of course, you know that an actual blackjack hand can have more than five cards without busting, but I assume that this was a test for correctly assigning the value of 11 or 1 to aces.

pbuk · Jan 24, 2024

RayDonaldPratt said:

Barring any syntax issues, it is a clever piece of logic.

Except it doesn't work for e.g.

DrClaude said:

Your algorithm may not work properly when there are more than one ace, for instance "T A A".

Blackjack program in javascript

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