Quick Sort Error: stack around the variable was corrupted?

Question

I am implementing a quick sort function for class. We have to do it the same way she taught us in class with her pseudocode, or else we dont get credit.

I am getting a runtime error that says "Stack around the variable 'quickArray' was corrupted"

I played with the debugger ,and still cannot figure out what the problem is. Im thinking that it has something to do with my Partition() function, but Im not sure. Can anyone help? Iv posted the main(), QuickSort(), and Partition() function below.

int main()
{


int quickArray[10] = { 5 ,99, 32, 4, 1, 12, 15 , 8, 13, 55};
int P = quickArray[0];
int R =quickArray[9];

QuickSort(quickArray,P,R);
return 0;

}

..........................................................................................

void QuickSort(int ar2[],int P, int R)
{
int Q;

if( P < R )
{
    Q =  Partition(ar2,P,R);
    QuickSort(ar2,P,Q-1);
    QuickSort(ar2,Q+1,R);
}

}

...........................................................................................

int Partition(int ar2[],int P, int R)
{
int x = ar2[R];
int i = P-1;
int temp;

for(int j = P; j <= R-1; j++)
{
    if( ar2[j] < x  )
    {
        i = i +1;
        temp = ar2[i];
        ar2[i] = ar2[j];
        ar2[j] = temp;
    }

    temp = ar2[R];
    ar2[R] = ar2[i+1];
    ar2[i+1] = temp;
}

return (i+1);
}

Answer 1

You are passing the actual elements of the array not the indexes, a quick way to have debugged this would be a cout at the top of QuickSort like so:

void QuickSort(int ar2[],int P, int R)
{
   std::cout << "P: " << P << " R: " << R << std::endl ;
   ...

and also a cout after the Partition call:

  Q =  Partition(ar2,P,R);

  std::cout << "QS: Q= " << Q << std::endl ;

the fix would be to call QuickSort from main like so:

 QuickSort(quickArray,0,9);

Spending some time with the debugger in the long term will help you spot these bugs much faster.