WAP to Find Two elements in Array whose sum is closest to zero

Algorithm
1) Sort all the elements of the array.
2) Find the index of first positive element, this is initial value of right index r.
3) Initialize: left index l = r – 1. min_sum = INT_MIN
4) In a loop, look for the candidates by comparing sum with minimum sum. If arr[l] + arr[r] becomes negative then increment the right index r, else decrement left index l.

#include
#include
#include


void quickSort(int *, int, int);

/* Function to print pair of elements having minimum sum */
void minAbsSumPair(int arr[], int arr_size)
{
int l, r = 0, min_sum, sum = 0, min_l, min_r;

/* Array should have at least two elements*/
if(arr_size < 2)
{
printf("Invalid Input");
return;
}

/* Sort the elements */
quickSort(arr, 0, arr_size-1);

/* Find the first positive element. Note that we have condition "r < arr_size -1"
-1 is there to handle the cases when all elements are negative */
while(arr[r] < 0 && r < arr_size - 1)
r++;

/* If all elements are positive then first two elements
are the minimum sum elements */
if(r == 0)
{
printf(" The first two elements %d and %d have minimum sum",
arr[0], arr[1]);
return;
}

/* Start looking for the pair from the first positive element
and last negative element */
l = r - 1;
min_sum = arr[l] + arr[r];
min_l = l; /* min_l is for the left element of minimum sum pair*/
min_r = r; /* min_r is for the right element of minimum sum pair*/
while(l >= 0 && r < arr_size)
{
sum = arr[l] + arr[r];

/*If abs(sum) is less then update the result items*/
if(abs(sum) < abs(min_sum))
{
min_sum = sum;
min_l = l;
min_r = r;
}
if(sum < 0)
r++;
else
l--;

printf (" %d %d %d \n ",min_sum,l,r);
}

printf(" The two elements whose sum is minimum are %d and %d",
arr[min_l], arr[min_r]);
}

/* Driver program to test above function */
int main()
{
int arr[] = {1, 60, -10, 70, -80, 85};
minAbsSumPair(arr, 6);
getchar();
return 0;
}

/* FOLLOWING FUNCTIONS ARE ONLY FOR SORTING
PURPOSE */
void exchange(int *a, int *b)
{
int temp;
temp = *a;
*a = *b;
*b = temp;
}

int partition(int arr[], int si, int ei)
{
int x = arr[ei];
int i = (si - 1);
int j;

for (j = si; j <= ei - 1; j++)
{
if(arr[j] <= x)
{
i++;
exchange(&arr[i], &arr[j]);
}
}

exchange (&arr[i + 1], &arr[ei]);
return (i + 1);
}

/* Implementation of Quick Sort
arr[] --> Array to be sorted
si --> Starting index
ei --> Ending index
*/
void quickSort(int arr[], int si, int ei)
{
int pi; /* Partitioning index */
if(si < ei)
{
pi = partition(arr, si, ei);
quickSort(arr, si, pi - 1);
quickSort(arr, pi + 1, ei);
}
}

Tim Complexity O(nlogn)
Space Complexity O(1)
Run Here https://ideone.com/Y4sk0