Question

 var num = [1,1];
 var total = 0;
 var i = num.length;
 do {
    i++;
    num[i] = num[num.length-1] + num[num.length-2];
    total+=num[i];
    console.log(total);
 }
 while(num[num.length] < 4000000);

I’ve been working on the Project Euler questions for a day or two now to hopefully expand my knowledge and usefulness. On the second question I’ve been figuring out a (bad) way to get the fibonacci sequence. However my code will print “2” to console as it SHOULD but then stopping. Another issue I have is that just using the “while(X IS TRUE/FALSE) { DO STUFF }” just won’t work. Not a clue why.

I’m probably just making dumb mistakes but somebody please enlighten me 🙂

Answer 1

Your num array has 2 elements, therefore num.length (and also i) are 2. The 1st statement in your do block is i++. Now i is 3.

You’re setting num[3], which means num is now [1, 1, undefined, 1].

Also, in your while, you are checking num[num.length]. Since arrays are zero-indexed, this will never work, as num.length is now 4.

What I suggest is: increment i after setting the element. So, you push a new element, then increment the length counter.

var num = [1, 1],
    total = 0,
    i = 2;  // we already know the length, no need to get it
do {
    // we don't need the i++ here
    num[i] = num[i - 1] + num[i - 2]; // add the last 2 elements to the end
    total += num[i];
    console.log(total);
}
while (num[i++] < 4000000);  // "i++" increments i and returns its old value