CODEWITHSUNDEEP
javascriptnan
Jonathan Lam
Jonathan Lam

Reputation: 17351

Why is NaN value outputted?

I'm trying to solver Project Euler #8. It asks to find the largest product of 13 consecutive digits in the following 1000-digit number. Here is my code (in JavaScript):

var bigNumber = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
for(var i = 0, largest = 0; i < 987; i++) {
  for(var j = 0, product = 1; j < 13; j++)
    product *= parseInt(bigNumber.substring(i*13+j, i*13+j+1));
  largest = Math.max(largest, product);
}

The answer is stored in largest. For some reason, largest is NaN, and I do not know why.

I've checked all the data types of all the numbers, especially product and largest, and they always turn up as "number." Their values are never infinity, which may also cause a NaN value.

I was also thinking maybe the products might be too large JavaScript to handle, but I thought it might have thrown a specific error for that.

What is causing this error and how should I solve it?

Upvotes: 2

Views: 583

Answers (3)

Scott Marcus
Scott Marcus

Reputation: 65808

The NaN problem is due to the way you are calculating which character you need to parseInt on. If you modify the code and keep a watch on largest, you'll see it takes on a value of Infinity, rather than NaN:

var bigNumber = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
var largest = 0;
var product = 1;
for (var i = 0; i < 999; i++) {

  for (var j = 0; j < 13; j++) {

    //Your original code produces NaN error:
    product *= parseInt(bigNumber.substring(i * 13 + j, i * 13 + j + 1));

    // This (more simple code) produces Infinity:
    product *= parseInt(bigNumber.charAt(j));
  }

  largest = Math.max(largest, product);

}

Upvotes: 0

Ivan
Ivan

Reputation: 10372

If you console.log(parseInt(bigNumber.substring(i*13+j, i*13+j+1))); you will see that it will print NaN.

The problem is that your substring is out of bounds.

Upvotes: 5

djechlin
djechlin

Reputation: 60748

I was also thinking maybe the products might be too large JavaScript to handle, but I thought it might have thrown a specific error for that.

Really? It would be very strange to me for a language to support Infinity and throw an error instead of use it.

There's some simple ways to test this for yourself:

for (var i = 0; ; i = i*2) console.log(i); // will eventually print Infinity

(Plus actual documentation.)

Upvotes: 0

Related Questions