---
title: Nesting For Loops
---
## Nesting For Loops
Remember to use Read-Search-Ask if you get stuck. Try to pair program :busts_in_silhouette: and write your own code :pencil:
:checkered_flag: Problem Explanation:
If you have a multi-dimensional array, you can use the same logic as the prior waypoint to loop through both the array and any sub-arrays.
Here is an example:
```
var arr = [
[1,2], [3,4], [5,6]
];
for (var i=0; i < arr.length; i++) {
for (var j=0; j < arr[i].length; j++) {
console.log(arr[i][j]);
}
}
```
This outputs each sub-element in arr one at a time. Note that for the inner loop, we are checking the length of arr[i], since arr[i] is itself an array.
- Modify function
multiplyAll so that it multiplies the product variable by each number in the sub-arrays of arr.
- Make sure the second for loop is nested inside the first.
Relevant Links
:speech_balloon: Hint: 1
Make sure to check with length and not the overall array.
try to solve the problem now
:speech_balloon: Hint 2
Use both i and j when multiplying the product.
try to solve the problem now
:speech_balloon: Hint 3
Remember to use arr[i] when you multiply the sub-arrays with the product variable.
try to solve the problem now
Spoiler Alert!
Solution Ahead!
:beginner: Basic Code Solution:
```
function multiplyAll(arr) {
var product = 1;
// Only change code below this line
for(var i=0; i < arr.length; i++){
for (var j=0; j < arr[i].length; j++){
product = product * arr[i][j];
}
}
// Only change code above this line
return product;
}
// Modify values below to test your code
multiplyAll([[1,2],[3,4],[5,6,7]]);
```
:rocket: Run Code
Code Explanation:
- We check the length of
arr in the i for loop and the arr[i] length in the j for loop.
- We multiply the
product variable by itself because it equals 1, and then multiply it by the sub-arrays.
- The two sub-arrays to multiply are
arr[i] and j.
:clipboard: NOTES FOR CONTRIBUTIONS:
- :warning: DO NOT add solutions that are similar to any existing solutions. If you think it is similar but better, then try to merge (or replace) the existing similar solution.
- Add an explanation of your solution.
- Categorize the solution in one of the following categories — Basic, Intermediate and Advanced. :traffic_light:
- Please add your username only if you have added any relevant main contents. (:warning: DO NOT remove any existing usernames)
See :point_right: Wiki Challenge Solution Template for reference.