Thread: what's wrong with this selection sort program code

Code:

# include <stdio.h>

int selection (int sort[], int n)
{
  int i,j;

  for (i=0; i<n; i++)
  {
    for (j=i+1; j<n; j++)
    { 
      if (sort[j] < sort[i])
        sort[i] = sort[j];
    }
  }

return ;
}

int main (void)
{
  int a[50],n,i;
  
  printf ("Enter number of elements\n");
  scanf ("%d",&n);

  printf ("Enter elements\n");
  for (i=0;i<n;i++)
  scanf ("%d",&a[i]);

  selection (a,n);
  
  for (i=0;i<n;i++)
  printf("%d \t",a[i]);
  printf("\n");
}

I am getting the following output.. Its weird

PHP Code:

Enter number of elements
5
Enter elements
3 5 4 1 2
1     1     1     1     2 


Actually why there is a need to swap ?
Actually, if you observe my code,

Code:

if (sort[j] < sort[i])
        sort[i] = sort[j];

if any element a[j] is less than the first element a[i], a[i] element is replaced with a[j] element.. thats what we wanted right !

Yes and what happens to the element that is replaced?

A[i] = 10
A[j] = 20

a[j] = a[i] ... both now equal 10 ... and what happened to the 20?

Yes you need to swap... not merely assign... that's why you got all those 1s...

In selection sort, you're supposed to find the maximum or minimum element and swap it in place. This creates a sorted subarray, and you just keep doing that until there are no more unsorted elements.

Oh! I got the point what you are saying ..
That means I need to assign a[j] value to a[i] and a[i] value to a[j] .. right ?
it this right >>

Code:

if (a[j] < a[i])
{
   swap = a[i]; 
   a[i] = a[j];
   a[j] = swap;

For the above logic i have re written ,, I am getting the following output..

Code:

Enter number of elements
5
Enter elements
 3 5 4 2 1
1 	2 	4 	5 	15269876

why there is still an error ??

The above program looks like this after re writing the code

Code:

# include <stdio.h>

int selection (int sort[], int n)
{
  int i,j,swap;

  for (i=0; i<n; i++)
  {
    for (j=i+1; j<n; j++)
    { 
      if (sort[j] < sort[i])
       // sort[i] = sort[j];
        swap = sort[i]; 
        sort[i] = sort[j];
        sort[j] = swap;
    }
  }

return ;
}

int main (void)
{
  int a[50],n,i;
  
  printf ("Enter number of elements\n");
  scanf ("%d",&n);

  printf ("Enter elements\n");
  for (i=0;i<n;i++)
  scanf ("%d",&a[i]);

  selection (a,n);
  
  for (i=0;i<n;i++)
  printf("%d \t",a[i]);
  printf("\n");
}

I got it guys .. Thanks for Helping .

You're still not finding the maximum or minimum number. Find the biggest or smallest thing with one loop, then right when your done with that, swap it into its sorted position (on the left or right of the array). Then that element is sorted; you do that for each element.

Originally Posted by iMalc

Well no you didn't actually.
You got something that sorts, but it isn't Selection Sort. Selection Sort performs the swap in the outer loop, not within the inner loop.
The sorting algorithm you have, whilst often stumbled upon, doesn't have a well-known name. I call it "Simple Sort".

Hi Imalc, that is how I learned selection sort as well, sort in the inner loop. Would you mind explaining how to do the sort in the outer loop?

Originally Posted by dolfaniss

Hi Imalc, that is how I learned selection sort as well, sort in the inner loop. Would you mind explaining how to do the sort in the outer loop?

iMalc doesn't need to explain it if you manage to Google "selection sort". The Wikipedia article shows it nicely.

Originally Posted by anduril462

iMalc doesn't need to explain it if you manage to Google "selection sort". The Wikipedia article shows it nicely.

Thanks!