Use it like this,
Array indexes should start from 0, that is why I have introduced another variable j=0
var numbers = [];
var sum = 0;
for (var i = 0, j = 0; i <= 100; i = i + 3, ++j) {
numbers[j] = i;
}
Update
First Issue:
In your code, ie. below code of yours,
for (var i = 0; i <= 100; i = i + 3) {
numbers[i - 1] = i;
}
In the first iteration,
i = 0;
numbers[0-1] = i // i.e numbers[-1] = 0;
and in your second loop, you are starting the index from 0
for (var index = 0; index < 100; index++) {
Second issue:
Also, if you don't use a sequential counter to fill the Array, you will end with undefined
values for the ones you did not fill.
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/dE18M.png)
If you notice, the output after the loop, it says numbers.length = 99
which is wrong it will not have that many items in it.
Third Issue:
In below code, even if you introduce a sequential counter, this is still wrong
for (var i = 0; i <= 100; i = i + 3) {
numbers[i - 1] = i;
}
because i
should start with 3 instead of 0, otherwise you will end up with 34 elements in the array because numbers[0]
will be 0;
Fourth Issue:
In this code,
for (var index = 0; index < 100; index++) {
document.write("<br/>" + numbers[index]);
sum = sum + i;
}
You don't actually have to loop it till 100, you already have the numbers array filled, so you just need to use numbers.length
, like this
var len = numbers.length;
for (var index = 0; index < len; index++) {
document.write("<br/>" + numbers[index]);
sum = sum + i;
}
A better way to write this
var numbers = [];
for (var i = 3, j=0; i <= 100; i = i + 3, j++) {
numbers[j] = i;
}
var sum = numbers.reduce((a, b) => a+b);
console.log(sum);
The line var sum = numbers.reduce((a, b) => a+b);
uses Array.reduce() method.
i - 1
will be-1
in the first iteration. Incrementingi
by3
and using it as array index will cause holes in the array.numbers
won't have100
elements, so you should not iterate over it from0
to100
. What do you thinki
is insum = sum + i;
?