# Credit Card Checker code question

Hey everybody!

So I’m working on the Credit Card Checker project at the moment and just “finished” task number 4.

``````// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9];
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6];
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5];
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6];

// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5];
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3];
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4];
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5];
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4];

// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4];
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9];
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3];
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3];
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3];

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];

const validateCard = array => {
for (let i = array.length - 2; i>=0; i-=2){
let doubleNumber = array[i]* 2;
if (doubleNumber > 9){
array[i] = doubleNumber - 9;
}else {
array[i] = doubleNumber;
}
}
let sum = 0;
for(let i = 0; i < array.length; i++)
{
sum = sum + array[i];
}
if (sum % 10 === 0){
return true;
}else {
return false;
}
}

const findInvalidCards = nestedArray => {

const invalidCards = [];
for (let i = 0; i < nestedArray.length; i++){
let cards = nestedArray[i];
if (validateCard(cards)== false){
invalidCards.push(cards);
}
}
return invalidCards;
}
console.log(findInvalidCards(batch));

``````

I’ve tested the “batch” array with the findInvalidCards() function and got the following list:

Then, just to make sure everything was working fine, I tested every single array with the validateCard() function. The 4th array, highlighted on the console ([ 3, 0, 2, 1, 2, 2, 5, 9, 3, 1, 5, 7, 5, 9, 6, 5 ]), returns true instead of false like the other ones…
Now, how could that be?
I’ve reviewed my code over and over but can’t seem to find the error…
Any ideas?

I think its because doing your `validateCard` function changes the contents of the array.
Note that printing out any of the arrays after doing `validateCard` or any other function that calls `validateCard` thus changes what’s in the array that represents each card.

One way to solve this problem is to do all the stuff in `validateCard` on a copy of the array instead of the original array.
I used something like

``````function validateCard(card) {
let array = Array.from(card);
``````

to start the function
by making a copy of the array that goes into the function

but there are many other ways to do that too.

I took the following from your code, to demonstrate that your function changes what’s in the array.

const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5]; console.log(invalid4); const validateCard = array => { for (let i = array.length - 2; i>=0; i-=2){ let doubleNumber = array[i]* 2; if (doubleNumber > 9){ array[i] = doubleNumber - 9; } else { array[i] = doubleNumber; } } let sum = 0; for(let i = 0; i < array.length; i++) { sum = sum + array[i]; } if (sum % 10 === 0){ return true; }else { return false; } } console.log(validateCard(invalid4)); console.log(invalid4);
1 Like

That was exactly it! I’ve tested all the arrays again and this time all of them returned false, thanks for your help mate!