Simple for loop is going infinite and I can't tell why

Question

for (var i = 10; i < 41; i+2) {
    console.log(i);
}

I am learning basic javascript and when I ran this on chrome, it crahsed. I think the loop going infinite but I don't understand why.

But when I change i + 2 to i++, it works fine.

I am trying to print out even numbers between 10 and 40 that's why I changed i + 2 to i++.

Am I not allowed to make i increment by 2?

Possible duplicate of [Can a for loop increment/decrement by more than one?](https://stackoverflow.com/questions/12809776/can-a-for-loop-increment-decrement-by-more-than-one) — Mans, Aug 17 '18 at 19:23

score 6 · Answer 1 · answered Aug 17 '18 at 19:21

6

You never change the value of i. Your expression is not an assignment of a value to i.

i += 2

for (var i = 10; i < 41; i += 2) {
    console.log(i);
}

answered Aug 17 '18 at 19:21

Nina Scholz

score 1 · Answer 2 · answered Aug 17 '18 at 19:22

1

Try this:

for (var i = 10; i < 41; i = i+2) {
    console.log(i);
}

or

for (var i = 10; i < 41; i +=2) {
    console.log(i);
}

answered Aug 17 '18 at 19:22

Mans

score 1 · Answer 3 · edited Aug 17 '18 at 19:24

1

You need to store the value back into the variable.

                         ↓↓
for (var i = 10; i < 41; i=i+2) {
    console.log(i);
}

edited Aug 17 '18 at 19:24

answered Aug 17 '18 at 19:22

mariamelior

I removed the asterisks from the code. They were meant to call attention to your change, but might be confusing to beginner programmers, who could easily misinterpret the asterisks as part of the code. – Aug 17 '18 at 19:27

score 1 · Answer 4 · answered Aug 17 '18 at 19:22

1

Just writing i+2 calculates the new value, but it doesn't store it back in the variable.

To increment i by 2, you need to write:

i = i + 2

or the shorthand:

i += 2

It works when you write i++ because that's short for

i = i + 1

answered Aug 17 '18 at 19:22

Barmar

4 Answers4