Is this true?

Question

I found this question in JS challenge mode :
var x;
for(i=0; i<10; i++){
for(j=0; j<=2; j++){
++x;
}
}
alert(x);
//the right answer was 30

I'm wondering how it works, it hurts my mind (please stop this madness) could someone please help? thanks.

Answer 1

Ah, that would be since it's not initialized.

var x = 0;

Would fix it.

Answer 2

i varies from 0 to 9 => 10 values
j varies from 0 to 2 => 3 values
There will be 30 iterations in total and x is increased by 1 in each iteration. So, output is 30.

Answer 3

Inner loop runs 3 times.
Outer loop runs 10 times.
3 x 10 = 30. (itterations)

Essentially, the inner loop finishes before the outer loop continues.

So it will run like so:

i = 0, j = 0.
i = 0, j = 1
i = 0, j = 2

Then,
i = 1, j = 0
i = 1, j = 1
i = 1, j = 2

etc...
Until the outer loop is finished.
(When i < 10 is false)

Answer 4

but alert(x) returns Not a Number, how is it?

Answer 5

:D problem solved... thank you @Rrestoring faith
and of course you too Mr. Krishna. Thank you so much