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

Kishan S
Kishan S
15,410 Points
Posted by Kishan S
Kishan S
15,410 Points

Is this Correct? Any simpler alternative using while statement?

Any Thoughts?

script.js 
var temperatures = [100,90,99,80,70,65,30,10];
var l = temperatures.length;
var i = 0;
while(l >= 0) {
  console.log(temperatures[i]);
  l-=1;
  i+=1;
}
index.html 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JavaScript Loops</title>
</head>
<body>
<script src="script.js"></script>
</body>
</html>

3 Answers

Andrews Gyamfi
Andrews Gyamfi
Courses Plus Student 15,658 Points

There is an Off-by-one error in your loop. This is how your code currently runs (I actually used Codepen.io to add some testing/debugging the code)

Modified Code:

var temperatures = [100,90,99,80,70,65,30,10];
var l = temperatures.length;
var i = 0;
while(l >= 0) {
  document.write(temperatures[i] + ", ");
  /* debugging code*/
  document.write("length: " + l + " | " + "index: " + i + "<br/>");

  /* loop counter increments */
  l-=1;
  i+=1;
 }

Output: 

100, length: 8 | index: 0
90, length: 7 | index: 1
99, length: 6 | index: 2
80, length: 5 | index: 3
70, length: 4 | index: 4
65, length: 3 | index: 5
30, length: 2 | index: 6
10, length: 1 | index: 7
undefined, length: 0 | index: 8

An array index starts from 0 to its length minus 1. In your code, you used the comparison 

while(l >= 0)

However, as per the above output, when your length (l variable) has been reduced to 0 your index (i variable) would have incremented to 8 which is 'undefined' or null as your array only has eight elements.

Solution: change while(l>=) to while(l > ) i.e remove '=' 

var temperatures = [100,90,99,80,70,65,30,10];
var l = temperatures.length;
var i = 0;
while(l > 0) {
  document.write(temperatures[i] + ", ");
  /* debugging code*/
  document.write("length: " + l + " | " + "index: " + i + "<br/>");

  /* loop counter increments */
  l-=1;
  i+=1;

}

Output: 

100, length: 8 | index: 0
90, length: 7 | index: 1
99, length: 6 | index: 2
80, length: 5 | index: 3
70, length: 4 | index: 4
65, length: 3 | index: 5
30, length: 2 | index: 6
10, length: 1 | index: 7

Hope this helps :) Cheers!

Rich Donnellan
MOD
Rich Donnellan
Treehouse Moderator 27,696 Points
Rich Donnellan
Rich Donnellan
Treehouse Moderator 27,696 Points

No, this isn't correct. The l (length) variable should not be decremented at all.

Check out the for loop; this does exactly what you're asking for (pun intended).

Provided code rewritten with for loop:

var temperatures = [100, 90, 99, 80, 70, 65, 30, 10];
for (var i = 0; i < temperatures.length; i++) {
  console.log(temperatures[i]);
}
Kishan S
Kishan S
15,410 Points
Kishan S
Kishan S
15,410 Points

Yes I Know that. but how to use while loop in that?

Jacie Fortune
Jacie Fortune
8,969 Points
Jacie Fortune
Jacie Fortune
8,969 Points

You shouldn't decrement l as the length of the array does not change. Here it is using a while loop. <code> var temperatures = [100, 90, 99, 80, 70, 65, 30, 10]; var i = 0; while (i < temperatures.length) { console.log(temperatures[i]); i += 1; } </code>