Bubble sort not swapping elements of array in Javascript

Question

I am creating a simple program that should utilize the bubble sort algorithm to sort a list of numbers in ascending order.

Just for testing purposes I have added the line alert(unsortedNumbers);and as you can see if you run it, the numbers do not change order no matter how many passes the algorithm does.

The program seems to be stuck in an infinite loop, as 'Another pass' is printed to the console repeatedly. As instructed by this line console.log("Another pass");

As with the bubble sort algorithm, once it does not have to swap any terms on a certain pass, we know this is the sorted list, I have created the variable swapped, however it looks like this is always 1. I think this may be caused by the swapArrayElements() function not swapping the terms.

Why is the function not swapping the index of the terms within the array?

(Code does't seem to run properly on SO's code snippet tool, may have to copy into notepad document)

function main(){

  var unsortedNumbers =[7,8,13,1,6,9,43,80]; //Declares unsorted numbers array
  alert(unsortedNumbers);
  var swapped = 0;
  var len = unsortedNumbers.length;

  function swapArrayElements(index_a, index_b) { //swaps swapArrayElements[i] with swapArrayElements[ii]
    var temp = unsortedNumbers[index_a];
    unsortedNumbers[index_a] = unsortedNumbers[index_b];
    unsortedNumbers[index_b] = temp;
  }

  function finish(){
    alert(unsortedNumbers);
  }

  function mainBody(){
    for(var i =0;i<len;i++){
      var ii =(i+1);
      if (unsortedNumbers[i]>unsortedNumbers[ii]){
        console.log("Swap elements");
        swapArrayElements(i,ii);
        swapped=1; // Variable 'swapped' used to check whether or not a swap has been made in each pass
      }
      if (ii = len){
        if (swapped = 1){ // if a swap has been made, runs the main body again
          console.log("Another pass");
          alert(unsortedNumbers); //Added for debugging
          swapped=0;
          mainBody();
        }else{
          console.log("Finish");
          finish();
        }
      }
    }
  }



  mainBody();
}

<head>
</head>
<body onload="main()">
</body>

You have error in your code if (ii = len){ and if (swapped = 1){ it should be double equal. — jcubic
– jcubic, Commented Apr 27, 2015 at 9:14
@jcubic Thanks for spotting this, can you write this as an answer and I'll mark as best answer. — Toby Cannon
– Toby Cannon, Commented Apr 27, 2015 at 9:16
@TobyCannon i think there is more simple ways to do the bubblesort.. don't know if it will fit your needs .. nczonline.net/blog/2009/05/26/… — Joel Almeida
– Joel Almeida, Commented Apr 27, 2015 at 9:17
@JoelAlmeida Thanks for that link Joel, certainly looks a more efficient way of doing it! This was just a first revision to try and get the logic behind it, I will not work on more efficient methods of writing it. — Toby Cannon
– Toby Cannon, Commented Apr 27, 2015 at 9:20

Toby Cannon · Accepted Answer · 2015-04-27 09:44:13Z

2

You have an error in your code:

if (ii = len) {

and also

if (swapped = 1){

it should be double equal

edited Apr 27, 2015 at 9:44

Toby Cannon

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answered Apr 27, 2015 at 9:18

jcubic

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Comments

Vijay · Accepted Answer · 2015-04-27 09:35:47Z

1

Invalid condition check causing infinite loop:

if (ii = len) & if (swapped = 1) should have == or === operator. This is causing infinity loop.

NOTE: Your code is not appropriate as per the best practices to avoid global variables. You should not use global variables and try passing variables and returning them back after processing.

Refer this for avoiding globals.

edited Apr 27, 2015 at 9:35

answered Apr 27, 2015 at 9:30

Vijay

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