CODEWITHSUNDEEP
javascriptnumbers
mstorm
mstorm

Reputation: 245

JavaScript Condition evaluates to false?

I am currently trying to get familiar with JavaScript through solving the Project Euler tasks. In the following snippet, I am trying to get the sum of all even fibonacci numbers below 4.000.000. 

var sum = 0;
var fibNums = [1, 2];
for (var i = 2; fibNums[i] < 4000000; i++) {
    fibNums[i] = fibNums[i - 1] + fibNums[i - 2];
    sum += fibNums[i] % 2 == 0 ? fibNums[i] : 0;
}
console.log(sum);

My problem is that fibNums[i] < 4000000 evaluates to false, even on the first run. How does that come?

Upvotes: 0

Views: 67

Answers (2)

Mitul
Mitul

Reputation: 3437

var sum = 0;
var fibNums = [1, 2, 0];

for (var i = 2;fibNums[i] < 4000000; i++) {
    fibNums[i] = fibNums[i-1] + fibNums[i-2];
    sum += fibNums[i] % 2 == 0 ? fibNums[i] : 0;
    fibNums.push(fibNums[i]); 
}

alert(sum);

Upvotes: 0

VisioN
VisioN

Reputation: 145458

In short: (fibNums[i = 2] === undefined), whereas (undefined < 40000 === false).

Longer:

You start your for loop with var i = 2, while fibNums array contains only 2 elements and has indexes starting with 0. Hence, fibNums[2] will be undefined. In JavaScript undefined is never less than a number, as when you compare any number with undefined it will always be false.

Upvotes: 4

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