freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/basic-javascript/counting-cards/index.md

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Counting Cards

Remember to use Read-Search-Ask if you get stuck. Try to pair program and write your own code

Problem Explanation:

In the casino game Blackjack, a player can gain an advantage over the house by keeping track of the relative number of high and low cards remaining in the deck. This is called card counting.

Having more high cards remaining in the deck favors the player. Each card is assigned a value according to the table below. When the count is positive, the player should bet high. When the count is zero or negative, the player should bet low.

Value	Cards
+1	2, 3, 4, 5, 6
0	7, 8, 9
-1	10, 'J', 'Q', 'K','A'

You will write a card counting function. It will receive a card parameter and increment or decrement the global count variable according to the card's value (see table). The function will then return a string with the current count and the string Bet if the count is positive, or Hold if the count is zero or negative. The current count and the player's decision (Bet or Hold) should be separated by a single space.

• Change the code below // Only change code below this line and up to // Only change code above this line
• Ensure that you are editing the inside of the cc function.
• Use what you've learned to check the value of each card parameter passed into the function.
• Keep a running count of that number.
• If the final count is 1 or greater, return # Hold.
• If the final count is 0 or less, return # Bet.

Example Output:

• -3 Hold
• 5 Bet

Hint: 1

Use a switch (or else if) statement to count the value of each card.

try to solve the problem now

Hint: 2

Add/subtract the value of each card to variable count. If the card is worth 0, don't do anything.

try to solve the problem now

Hint: 3

After you've counted the cards, use an if statement to check the value of count. Also, make sure your return has a space between the number and the string.

try to solve the problem now

Spoiler Alert!

Solution ahead!

Basic Code Solution:

    function cc(card) {
      // Only change code below this line
      switch(card){
        case 2:
        case 3:
        case 4:
        case 5:
        case 6:
          count++;
          break;
        case 10:
        case "J":
        case "Q":
        case "K":
        case "A":
          count--;
          break;
      }
      if (count > 0){
        return count + " Bet";
      } else {
        return count + " Hold";
      }
      // Only change code above this line
    }

Code Explanation:

• Check the value of each card via a switch statement.
• The variable count:
  • Increases by 1 if the card is a 2, 3, 4, 5, or 6.
  • Since 7, 8, and 9 aren't worth anything, we ignore those cards in our switch statement.
  • Decreases by 1 if the card is a 10, 'J', 'Q', 'K', or 'A'.
• Check the value of count and return the appropriate response.

Example Run

• cc(2); runs.
• The switch statement hits case 2, jumps down and adds 1 to the variable count.
• The switch statement then hits the break and cc(3); runs.
• This cycle continues until the final call is made, cc('A');.
• After the switch statement, the if statement checks count, which is now 0.
• This then drops down to the else statement, which will return 0 Hold.

Note: As mentioned earlier, the switch statement could have also been an else if statement.

Additional code solution:

function cc(card) {
  // Only change code below this line
  var regex = /[JQKA]/;
  if (card > 1 && card < 7){count++;}
  else if (card === 10 || String(card).match(regex)){count--;}

  if (count > 0) return count + " Bet";
  return count + " Hold";

  // Only change code above this line
}

· Run code at repl.it.

Code explanation

· The function first evaluates if the condition card is a value greater than 1 and lower than 7, in which case it increments count by one. · Then if the card is 10 or higher it decrements count by one. · The variable regex is a regular expression representing values (letters) for the higher cards. · The else statement checks those values with the || (logical OR) operator; first for 10 and then for any string that matches the regular expression using String.match().

Resources

• Card counting at Wikipedia
• Challenge: Selecting from many options with Switch Statements
• Challenge: Chaining If Else Statements
• Challenge: Increment a Number with Javascript