归并排序问题

我正在制作各种排序算法的菜单，现在我被困在归并排序。我在点击执行按钮后遇到了一个错误。我在TextBox1中输入了5个数字，在TextBox2中输入了另外一组5个数字。它说索引超出了数组的边界。我在代码上标出了它出现的地方。知道是什么问题吗?

    private void ExeButton_Click(object sender, EventArgs e)
    {
        string[] numsInString = EntNum.Text.Split(' ');   //split values in textbox
        string[] numsInString1 = EntNum1.Text.Split(' ');
        for (int j = 0; j < numsInString.Length; j++)
        {
            a[j] = int.Parse(numsInString[j]);
        }
        for (int j = 0; j < numsInString1.Length; j++)
        {
            b[j] = int.Parse(numsInString1[j]);
        }
        {
            sortArray();
            Display();
        }
    }
    public void sortArray()
    {
        m_sort(0, 10 - 1);
    }
    public void m_sort(int left, int right)
    {
        int mid;
        if (right > left)
        {
            mid = (right + left) / 2;
            m_sort(left, mid);
            m_sort(mid + 1, right);
            merge(left, mid + 1, right);
        }
    }
    public void merge(int left, int mid, int right)
    {
        int i, left_end, num_elements, tmp_pos;
        left_end = mid - 1;
        tmp_pos = left;
        num_elements = right - left + 1;
        while ((left <= left_end) && (mid <= right))
        {
            if (a[left] <= a[mid])  //index was outside the bounds of the the array
            {
                b[tmp_pos] = a[left];
                tmp_pos = tmp_pos + 1;
                left = left + 1;
            }
            else
            {
                b[tmp_pos] = a[mid];
                tmp_pos = tmp_pos + 1;
                mid = mid + 1;
            }
        }
        while (left <= left_end)
        {
            b[tmp_pos] = a[left];
            left = left + 1;
            tmp_pos = tmp_pos + 1;
        }
        while (mid <= right)
        {
            b[tmp_pos] = a[mid];
            mid = mid + 1;
            tmp_pos = tmp_pos + 1;
        }
        for (i = 0; i < num_elements; i++)
        {
            a[right] = b[right];
            right = right - 1;
        }
    }

    private void ClearButton_Click(object sender, EventArgs e)
    {
        richTextBox1.Clear();
    }
    public void Display()
    {
        int i;
        String numbers = "";
        for (i = 0; i < 10; i++)
        numbers += a[i].ToString() + "       ";
        numbers += b[i].ToString() + "       ";
        richTextBox1.AppendText(numbers + "'n");
    }