void mergesort(int array_to_sort[], int left, int right)
{
    int splitpos;

    if (left < right)
    {
        // Partition the array into two subarrays, sort these subarrays recursively and then merge them into
        // a correctly sorted array.
        splitpos = (left + right) / 2;
        mergesort(array_to_sort, left, splitpos);
        mergesort(array_to_sort, splitpos + 1, right);
        merge(array_to_sort, left, splitpos, right);
        }
}

void merge(int array_to_sort[], int left, int splitpos, int right)
{
    int size_array1 = splitpos - left + 1;
    int size_array2 = right - splitpos;
    int array1[size_array1];
    int array2[size_array2];
    int i = 0;
    int j = 0;

    // Copy both sub-arrays to auxilary arrays.

    for (i = 0; i < size_array1; i++)
    {
        array1[i] = array_to_sort[left + i];
        }

        for (j = 0; j < size_array2; j++)
        {
        array2[j] = array_to_sort[splitpos + j + 1];
        }

        i = 0;
        j = 0;


        int k;

        for (k = left; k <= right; k ++)
        {
            if ( j = size_array2 )
            { 
            array_to_sort[k] = array1[i];
            i++; 
            }
            else if ( i = size_array1 )
            {
            array_to_sort[k] = array2[j];
            j++; 
            }
            else if (array1[i] <= array2[j])
            {
            array_to_sort[k] = array1[i];
            i++;
            }
            else
            {
            array_to_sort[k] = array2[j];
            j++;
            }
    }
}