Iterative Quick Sort

using System;
using System.Text;
using System.Windows.Forms;

namespace IterativeQuickSort
{
    public partial class frmSort : Form
    {
        private int nDataSz = 100000;
        private int[] TestData;
        private bool bSortUp;

        public frmSort()
        {
            InitializeComponent();

            bSortUp = optSortUp.Checked = true;
            btnDoSort.Enabled = false;

            numUpDnSz.Minimum = 2;
            numUpDnSz.Maximum = 1000000;
            numUpDnSz.Increment = 100000;
            numUpDnSz.Value = nDataSz;
        }

        private void GenerateExampleData()
        {
            int i;
            Random PRNG = new Random();

            btnDoSort.Enabled = false;

            Cursor Csr = this.Cursor;
            this.Cursor = Cursors.WaitCursor;

            nDataSz = (int)numUpDnSz.Value;
            TestData = new int[nDataSz];

            for (i = 0; i < nDataSz; i++)
                TestData[i] = PRNG.Next();

            DisplayDataToTextBox(tbxInput, TestData);
            tbxOutput.Text = "";
            btnDoSort.Enabled = true;

            this.Cursor = Csr;
        }

        private void btnDoSort_Click(object sender, EventArgs e)
        {
            Cursor Csr = this.Cursor;
            this.Cursor = Cursors.WaitCursor;

            IttvQuickSort iqs = new IttvQuickSort();
            iqs.SortData = TestData; // NB this is copied, ie by value, not by reference

            double Tmr = 0.0;
            Stopwatch.Start();

            if (!iqs.PerformSort(bSortUp))
                MessageBox.Show("Unknown error occurred in execution of sort");

            Stopwatch.Stop();
            Tmr = Stopwatch.time;
            lblTiming.Text = String.Format("{0:F} msec", Tmr);

            DisplayDataToTextBox(tbxOutput, iqs.SortData);

            this.Cursor = Csr;
        }

        private void DisplayDataToTextBox(TextBox tbx, int[] Data)
        {
            int i;
            StringBuilder sbData = new StringBuilder();

            for (i = 0; i < nDataSz; i++)
                sbData.AppendLine(Data[i].ToString());

            tbx.Text = sbData.ToString();
        }

        private void btnGenData_Click(object sender, EventArgs e)
        {
            GenerateExampleData();
        }

        private void optSortUp_CheckedChanged(object sender, EventArgs e)
        {
            if (!bSortUp)
            {
                bSortUp = true;
                tbxOutput.Text = "";
            }
        }

        private void optSortDn_CheckedChanged(object sender, EventArgs e)
        {
            if (bSortUp)
            {
                bSortUp = false;
                tbxOutput.Text = "";
            }
        }

        private void numUpDnSz_ValueChanged(object sender, EventArgs e)
        {
            btnDoSort.Enabled = false;
        }
    }
}