Different results getting array element inside while condition vs outside - c++

Question

I've been working on this quicksort code for a while now and cant figure out why I get different results based on where I get an array value. If I get the value of pivot outside of my loop it works fine, inside the loop it does not.
I've highlighted the difference between each function with some /*This works/doesnt*/ comments.
#include <stdio.h>
void quicksort(int * x, int left_limit, int right_limit) {
int left = left_limit;
int right = right_limit;
int pivot = x[(right + left) / 2]; /* This works */
while (left <= right) {
while (x[left] < pivot) { left++; } /* This works */
while (x[right] > pivot){ right--; } /* This works */
if (left <= right) {
int temp = x[left];
x[left] = x[right];
x[right] = temp;
left++;
right--;
}
}
if (left_limit < right)
quicksort(x, left_limit, right);
if (left < right_limit)
quicksort(x, left, right_limit);
}
void quicksortBROKEN(int * x, int left_limit, int right_limit) {
int left = left_limit;
int right = right_limit;
int pivot = (right + left) / 2; /* This doesnt */
while (left <= right) {
while (x[left] < x[pivot]) { left++; } /* This doesnt */
while (x[right] > x[pivot]){ right--; } /* This doesnt */
if (left <= right) {
int temp = x[left];
x[left] = x[right];
x[right] = temp;
left++;
right--;
}
}
if (left_limit < right)
quicksort(x, left_limit, right);
if (left < right_limit)
quicksort(x, left, right_limit);
}
int main() {
int x[] = {0,2,1,4,3,5,6,3,7,8,4,3,7,8};
quicksort(x, 0, 13);
for (int i = 0; i < 14; i++) {
printf("%d, ", x[i]);
}
printf("\n");
return 0;
}
What is wrong with the broken function?

Answer 1

In the broken version the value of the pivot (as opposed to its location) changes over the course of the function.

Answer 2

Debugger would probably show it to you best, but there is a distinct difference between the functions.
The first one takes a value from the array to the variable and doesn't change it.
The second one takes a position and compares the value on that position in the array each time, while modifying the array. If the array is modified on the position that is stored, naturally the comparisons differ.