void quicksort( int a[], int first, int last)
{
    int i = first;
    int j = last;
    int x = a[(first + last)/2];
    int tmp;
    FILE *output;

    output = fopen("sort3.txt", "w");

    do
    {
        while(a[i] < x)
             i++;

        while(a[j] > x)
             j--;

        if(i <= j)
        {
            tmp = a[i];
            a[i] = a[j];
            a[j] = tmp;

            i++;
            j--;
        }
    } while(i <= j);

    if(first < j) quicksort(a, first, j);
    if(last > i) quicksort(a, i, last);

    if(last > i)
    {
        for(i = 0; i <= 999; i++)
            fprintf(output, "%d\n", a[i]);
    }

}