Quicksort with heisenbug

gistfile1.txt

#include <stdio.h>
#include <stdlib.h>

void quicksort(int *array, int length);
void swap(int *a, int *b);
void print(int *array, int length);

int main()
{
    int test = -10; //demonstrates the heisenbug 
    // set j<=length in line 43 and watch test appear in the sorted array iff test < partition
    int input_array[] = {2, 1, 11, 17, 34, 3, -9}; // YOU MUST DECLARE LENGTH 
    int *array_ptr = &input_array[0];
    int LENGTH = 7;

    print(array_ptr, LENGTH);

    quicksort(array_ptr, LENGTH);

    print(array_ptr, LENGTH);

    return 0;
}

void quicksort(int *array, int length)
{

    int partition; // value of the partition element
    int i, j; // iterators 
    int r_len, l_len; // length of two arrays resulting from partition
    int *r_array, *l_array; // new pointers to arrays resulting from partition

    if (length < 2)
    {
        return; // terminate - you're done
    } 

    partition = *(array); //value of the partition element (here just taking first elem as partition)
    i = 1; // initialize to 1 because array[0] is the partition element

    for (j=1; j<=length; j++) // initialize to 1 because array[0] is the partition element
        // set j<=length instead of j<length to show the heisenbug
    {
        printf("In loop! i = %d, j = %d\n", i, j);
        print(array, length);
        if (*(array + j) < partition)
        {
            swap((array + i), (array + j));
            i++;
        }
    }

    print(array, length);

    swap(array, (array + i -1)); // places partition into correct spot

    printf("Swapped partition element\n");
    print(array, length);

    l_len = i - 1; //omit i - parition is already in right spot
    l_array = array;
    r_array = (array + i); // because array is already a pointer, this is just pointer arithmetic ... maybe
    r_len = length - i;

    printf("Right array:   ");
    print(r_array, r_len);
    printf("Left array:    ");
    print(l_array, l_len);

    quicksort(r_array, r_len);
    quicksort(l_array, l_len);

}

void swap(int *a, int *b)
{
    //this swap function passes in pointers and rearranges the underlying values.
    //printf("In swap %d %d\n", *a, *b); // dereference & print
    int temp; // temporary var to store while swapping
    temp = *a; // temp var gets the value of a
    *a = *b; // value of a gets the value of b
    *b = temp; // value of b gets the value of temp (originally a)
    //printf("After swap %d %d\n", *a, *b);
}

void print(int *array, int length)
{
    int i;
    for (i=0; i<length; i++)
    {
        printf("%d\t", *(array+i));
    }
    printf("\n");
}