# +- why should we use it?

Why do we have to use ±?
Shouldn’t + work to?

``````
// Setup
var myArray = [];
for (var i = 1; i <= 9; i += 2) {
myArray.push(i);
}

// Only change code below this line
``````
``````  **Your browser information:**
``````

User Agent is: `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36`

Challenge: Iterate Odd Numbers With a For Loop

You don’t use ±, that’s not a thing in programming languages.

I guess you mean `+=`?

So `let i = 0` is what happens to kick off the loop. You initialise a variable called `i`, assigning it the number 0.

`i <= 9` is the condition, this happens before each iteration of the loop: if it’s true, the code in the loop runs, if it’s false, the loop ends.

`i += 2` is what happens at the end of every iteration of the loop.

`i += 2` is shorthand for `i = i + 2`.

• `i` is 0. Is 0 <= 9? Yes, code runs. `i = 0 + 2`.
• `i` is 2. Is 2 <= 9? Yes, code runs. `i = 2 + 2`.
• `i` is 4. Is 4 <= 9? Yes, code runs. `i = 4 + 2`.
• `i` is 6. Is 6 <= 9? Yes, code runs. `i = 6 + 2`.
• `i` is 8. Is 8 <= 9? Yes, code runs. `i = 8 + 2`.
• `i` is 10. Is 10 <= 9? No, so loop ends.

If instead, you just used `i + 2`

• `i` is 0. Is 0 <= 9? Yes, code runs. `0 + 2` (no change to `i`).
• `i` is 0. Is 0 <= 9? Yes, code runs. `0 + 2` (no change to `i`).
• `i` is 0. Is 0 <= 9? Yes, code runs. `0 + 2` (no change to `i`).
• `i` is 0. Is 0 <= 9? Yes, code runs. `0 + 2` (no change to `i`).
• …and so on, forever
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