Implementation of Quick Sort C++ - c++

Question

I've learned about Quick Sort is a sorting algorithm which follows the principle of Divide and Conquer with average time complexity as n(log n) and worst time complexity as n^2.
Here I've selected middle element as pivot.
When it exceeds length of array then function returns the array.
I have used four functions to implement Merge Sort:
Quick Sort Functions
isSorted( ) returns true if array is sorted.
pivotPositioning( ) arrange pivot at it's ideal position.
quickSort( ) //wrapper function
quickSort( ) returns sorted array
Initial Pivot is selected as the middle element of the array by default argument.
It's giving an error, showing last element as -2 for even length of array (i.e. 4,8,10) after the sorting is done. I would like to know what's causing the error?
//C++ Code
#include<iostream>
void print(int *, int);
bool isSorted(int *arr, int high, int low=0)
{
for(int i=low; (i+1)<high; i++)
{
if(arr[i] > arr[i+1])
{
return false;
}
}
return true;
}
void pivotPositioning(int *arr, int high, int low)
{
for(int i=low; (i+1)<high; i++)
{
if(arr[i] > arr[i+1])
{
int temp = arr[i];
arr[i] = arr[i+1];
arr[i+1] = temp;
}
}
}
void quickSort(int *arr, int length, int pivot)
{
pivotPositioning(arr, pivot+1, 0);
//print(arr, length);
pivotPositioning(arr, length, pivot);
//print(arr, length);
}
int *quickSort(int *arr, int length)
{
int pivot = length/2;
quickSort(arr, length, pivot);
if (isSorted(arr, length) == false)
{
while (pivot > 0)
{
pivot--;
quickSort(arr, length, pivot);
}
while (pivot<length)
{
pivot++;
quickSort(arr, length, pivot);
}
}
return arr;
}
int main()
{
int length ;
std::cout<<"Enter length of the array: ";
std::cin>>length;
int arr[length] ;
for(int i=0; i<length; i++)
{
std::cout<<"Enter Element "<<(i+1)<<" : ";
std::cin>>arr[i];
}
quickSort(arr, length);
print(arr, length);
return 0;
}
void print(int *arr, int length)
{
std::cout<<"Sorted Array: ";
for(int i=0; i<length; i++)
{
std::cout<<arr[i]<<" ";
}
std::cout<<"\n";
}