Bubble sort in C: Function not changing array data

Question

Code:

#include <stdio.h>

void testSort(int values[], int n);

int main(void)
{
    int hs[] = {5,3,2,1,4};
    printf("Unsorted: %i %i %i %i %i\n", hs[0], hs[1], hs[2], hs[3], hs[4]);
    testSort(hs, 5);

    printf("Sorted: %i %i %i %i %i\n", hs[0], hs[1], hs[2], hs[3], hs[4]);
}

void testSort(int values[], int n)
{
    for (int i = 0; i < n-1; i++)
    {
        int hold;
        int current = values[i];
        int next = values[i + 1];

        if (current > next)
        { 
            hold = current;
            current = next;
            next = hold;
        }
    }
    return;
}

I'm trying to do bubble sort and right now it goes through the array once, but my question is: Why isn't my hs[] updating after calling function? The second printf shows that it remained the same.

EDIT: As mentioned, turns out I was changing data but of the copies. For some reason I when I created the variables current/next I felt as if they were representing values[i]/values[i+1] but in reality I was just creating new variable and passing the value of values[0] which is 5 and assigning it to current. Obviously leaving values[] unchanged. Thanks everyone

You need to swap values[i] with values[i+1]. All the code does is swap the copies in current and next. — user3386109
– user3386109, Commented Dec 9, 2016 at 9:39
@Fang You cannot pass an array by value, it decays into a pointer to its first element. — Quentin
– Quentin, Commented Dec 9, 2016 at 9:41
The function isn't changing the data, because it contains no code that changes the data... Surely you could figure this out yourself by spending a moment to read your own code. — Lundin
– Lundin, Commented Dec 9, 2016 at 9:58

molbdnilo · Accepted Answer · 2016-12-09 10:06:38Z

2

The problem is that you're only modifying the function's local variables, not the array's elements.

It's the same principle as why this program will print 1 and not 2:

int main()
{
    int array[] = {1};
    int x = array[0];
    x = 2;
    printf("array[0] = %d\n", array[0]);
    return 0;
}

You need to assign values to the array's elements:

void testSort(int values[], int n)
{
    for (int i = 0; i < n-1; i++)
    {
        if (values[i] > values[i+1])
        { 
            int hold = values[i];
            values[i] = values[i+1];
            values[i+1] = hold;
        }
    }
}

Once you've fixed this, you will notice that this function only works for some inputs.
Solving that bug is left as an exercise.

answered Dec 9, 2016 at 10:06

molbdnilo

67.1k3 gold badges46 silver badges90 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Sarika Koli · Accepted Answer · 2016-12-09 09:47:16Z

0

Please try below code:-

 void bubble_sort(int list[], int n){
      int c, d, t;
      for (c = 0 ; c < ( n - 1 ); c++)
      {
         for (d = 0 ; d < n - c - 1; d++)
          {
             if (list[d] > list[d+1])
             {
                 t         = list[d];
                 list[d]   = list[d+1];
                 list[d+1] = t;
             }
          }
     }
 }

answered Dec 9, 2016 at 9:47

Sarika Koli

7936 silver badges11 bronze badges

3 Comments

Jabberwocky Over a year ago

A little explanation might help here.

Sarika Koli Over a year ago

first you will try this code & check is it work or not.then I will explain it

M Oehm Over a year ago

@SarikaKoli: No, that's nonsense. You are making suggestions to change the code and therefore should explain them right away, not after someone else has verifies thetsolution is correct. (That's your job as answrer, by the way: To provide working code. Whether that is by being confident or by testing actual code doesn't matter.)

Collectives™ on Stack Overflow

Bubble sort in C: Function not changing array data

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related