# Challenge Project: Credit Card Checker - Loop Crash

Hello, I’m working on the Challenge Project: Credit Card Checker exercise and I’m a bit stuck on what it seems like a loop that goes on forever and crashes.

// 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, ]; // Add your functions below: function validateCred(arr) { let lastElement = arr.length - 1; var sum = 0; var double = 0; for (i = arr.length - 1; i >= 0; i--) { if (lastElement % 2 === 0) { if (i === arr.length - 1) { sum = sum + arr[i]; } else if (i % 2 === 1) { double = arr[i] * 2; if (double > 9) { double = double - 9; sum = sum + double; } else if (double <= 9) { sum = sum + double; } } else if (i % 2 === 0) { sum = sum + arr[i]; } } else if (lastElement % 2 === 1) { if (i === arr.length - 1) { sum = sum + arr[i]; } else if (i % 2 === 0) { double = arr[i] * 2; if (double > 9) { double = double - 9; sum = sum + double; } else if (double <= 9) { sum = sum + double; } } else if (i % 2 === 1) { sum = sum + arr[i]; } } } if (sum % 10 === 0) { return true; } else return false; } //console.log(validateCred(mystery5)); //const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8] function findInvalidCards(arr) { var invalidCards = []; for (i = 0; i < arr.length; i++) { if (!validateCred(arr[i])) { invalidCards.push(arr[i]); } } } //findInvalidCards(batch);

Everything goes well until I want to use the last function - findInvalidCards(). As soon as I run the last commented line, it goes in a loop.

Can anyone help me find what I’m doing wrong?

` for (let i = arr.length - 1; i >= 0; i--)`
` for (let i = 0; i < arr.length; i++)`