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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Iterating through an Array

Posted by micheleg
micheleg
3,808 Points

Unsure about this Arrays task

My brain just isn't registering this, I can't figure out how to do it. I've been following along but now I'm lost. Any explanations much appreciated. This is the question:

Use a for or while loop to iterate through the values in the temperatures array from the first item -- 100 -- to the last -- 10. Inside the loop, log the current array value to the console.

Thanks

script.js 
var temperatures = [100,90,99,80,70,65,30,10];

for ( i = 0; i >= 10; i += 1 ) {

  console.log( temperatures );
}
index.html 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JavaScript Loops</title>
</head>
<body>
<script src="script.js"></script>
</body>
</html>

2 Answers

Leandro Botella Penalva
Leandro Botella Penalva
17,618 Points
Leandro Botella Penalva
Leandro Botella Penalva
17,618 Points

Hi micheleg,

In the array there are 8 items in total and you want to loop through that items. First you need to know that arrays start to count from 0 so the first item corresponds to the index 0 and the last items to the index 7. The the loop would be "loop starting from index 0 while the index is less or equal to 7 (last index)" and that in code would be:

var temperatures = [100,90,99,80,70,65,30,10];

for (var i = 0; i <= 7; i++) {
  console.log(temperatures[i]);
}

To read a value from an array you use the array name and between square brackets you put the index or position you want to get, remember first position is always 0.

In the task you know how many items has the array but imagine you don't know the size of the array. Another way would be 

var temperatures = [100,90,99,80,70,65,30,10];

for (var i = 0; i < temperatures.length; i++) {
  console.log(temperatures[i]);
}

.length returns the number of items of an array, in this case you use less than but not equals to because the size is always one unit above the last index. In an array of 8 items, .length would return 8 but the last item index is 7 so we don't want to include the index 8 since it doesn't exist.

micheleg
micheleg
3,808 Points

Thank you so much! This makes sense and is actually simpler than I expected. Thank you for taking all this time.

Emre Karakuz
Emre Karakuz
9,162 Points
Emre Karakuz
Emre Karakuz
9,162 Points

First of all, the variable 'i' inside for loop should have proper limit for not indexing the elements outside of the loop. If an array have 10 items, varible 'i' should change 0 to 9. not 10 or something else.

In your code, 'i' starts from zero but the loop will run when i >= 10. Because of having a zero value in 'i', loop will never run.

To adjust proper limit for 'for' loop, use .length. its always better.

for ( i = 0; i < temperatures.length ; i += 1 )

in addition, you are targeting all of the array 'temperatures' with the console.log To target each item in the array, add [i] after temperatures like this :

console.log( temperatures[i] );
micheleg
micheleg
3,808 Points

Thank you! This is starting to make sense. :)