生成簽證碼

public partial class test1 : System.Web.UI.Page

{

    private char[] constant ={ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };

    protected void Page_Load(object sender, EventArgs e)

    {

        if (!Page.IsPostBack)

        {

            string VNum = GenerateRandom(5);

            Session["VNum"] = VNum;

            Validate_code(VNum);

        }

    }

    private  string GenerateRandom(int length)

        {

            System.Text.StringBuilder sb = new System.Text.StringBuilder(62);

            System.Random r = new Random();

            for(int i=0;i<length;i++)

            {

                sb.Append(constant[r.Next(62)]);

            }

            return sb.ToString();

        }

        private  void Validate_code(string sValue)

        {

            int gHeigth=Int32.Parse((sValue.Length * 11).ToString());

            System.Drawing.Bitmap Img = new System.Drawing.Bitmap(gHeigth,20);

            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(Img);

            g.DrawString(sValue, new System.Drawing.Font("Arial", 10), new System.Drawing.SolidBrush(System.Drawing.Color.Blue), 3, 3);

            System.IO.MemoryStream ms = new System.IO.MemoryStream();

            Img.Save(ms,System.Drawing.Imaging.ImageFormat.Png);

            Response.ClearContent();

            Response.ContentType="image/gif";

            Response.BinaryWrite(ms.ToArray());

            g.Dispose();

            Img.Dispose();

            Response.End();

        }

}