freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/basic-javascript/nesting-for-loops/index.md

title
Nesting For Loops

Nesting For Loops

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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

• Nest One Array Within Another Array
• Iterate Through An Array With A For Loop
• Accessing Nested Arrays

Hint: 1

Make sure to check with length and not the overall array.

try to solve the problem now

Hint 2

Use both i and j when multiplying the product.

try to solve the problem now

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!

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]]);

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.

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