What am i doing wrong here.

[versacestl]

problm fixed

[ltcmelo]

Aren't you missing a less than sign in the if condition of merge_sort?

if (p < r)
{
  //...
}

[versacestl]

Aren't you missing a less than sign in the if condition of merge_sort?

if (p < r)
{
  //...
}

yep sorry.. changed some variables.. code is how i have it currently..
still getting same issue..

[ltcmelo]

I found some errors on your implementation. Here's a fixed version, but you should check if there are still other errors. Hope you understand the notes in the code.

#include <algorithm>
#include <iostream>


void merge(int a[], int p, int q, int r)
{
    //Changed initialization to use q.[/color]
    int i = q + 1;
    int j = q;

    //Changed initialization to p instead of 0.
    int k = p;

    //What exactly is this for? 
    //int n = ((p- r) + 1);
    //int b[] = {n};    
    int b[10]; //Size of 10 just for the example.

    if (p < r)
    {	
        //And this?
        //b[n] = a[n];

        //You need to fill b accordingly. Perhaps that's what you were trying with the parts I didn't understand?
        for (; i > p; --i) 
          b[i-1] = a[i-1];
        for (; j < r; ++j) 
          b[r+q-j] = a[j+1];

        for (; k <= r; k++)
        {
            if ((i > q) || (j <= r&& b[j] <= b[i]))
            {
                a[k] = b[j];
                j = j - 1; //Subtract.
            }
            else 
            {
                a[k] = b[i];
                i = i + 1;
            }	
        }
    }
}

void merge_sort(int a[], int p, int r)
{
    if (p < r) 
    {
        int q=  ((p+ r) / 2);
        merge_sort(a, p, q);
        merge_sort(a, q+ 1, r); //r not q here.
        merge(a, p, q, r);
    }
}

int main()
{
    int v[] = {4, 7, 2, 1, 8, 6, 3, 5, 9, 0};
    merge_sort(v, 0, 9);
    std::copy(v, v + 10, std::ostream_iterator<int>(std::cout, " "));
    return 0;
}

[versacestl]

Is that working for you? Cause it's still blowing up for me

[ltcmelo]

Is that working for you? Cause it's still blowing up for me

Yes, it does. I get the sorted output.

In general, you should keep the original post even if it's been solved because it might help other people going through the same problem.