程序代码：

public partial class Form1 : Form
    {
        string text = "abcdefghijk";
        int len = 1;
        Timer timer = new Timer();
        public Form1()
        {
            InitializeComponent();
            timer.Interval = 500;
            timer.Enabled = true;
            timer.Tick += new EventHandler(timer_Tick);
        }

        void timer_Tick(object sender, EventArgs e)
        {
            if (len < text.Length)
            {
                label1.Text = text.Substring(0, len);
                len++;
            }
            else
            {
                len = 1;
                timer.Stop();
                Form f = new Form();
                f.ShowDialog();
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer.Start();
        }
    }