. NET generate random Verification Code

Create a new Web form named "RandomImage. aspx" to output an image containing four random verification codes. The characters are numbers or uppercase letters. It uses a basic knowledge: numbers 0 ~ 9 The corresponding ASCII code is 48 ~ 57, Letter ~ The ASCII code corresponding to Z is 65 ~ 90. When a Random verification code is generated, the program saves the verification code through Cookies for comparison when submitting the form.

The following is the RandomImage. aspx code:
Using System;
Using System. Data;
Using System. Configuration;
Using System. Collections;
Using System. Web;
Using System. Web. Security;
Using System. Web. UI;
Using System. Web. UI. WebControls;
Using System. Web. UI. WebControls. WebParts;
Using System. Web. UI. HtmlControls;
Using System. Drawing; // header file of the Graphics class

Public partial class RandomImage: System. Web. UI. Page
{
Protected void Page_Load (object sender, EventArgs e)
{
This. CreateCheckCodeImage (GenerateCheckCode ());
}
# Code generated by region web Form Designer
Override protected void OnInit (EventArgs e)
{
//
// CODEGEN: This call is required by the asp. NET web form designer.
//
InitializeComponent ();
Base. OnInit (e );
}

/// <Summary>
/// The designer supports the required methods-do not use the code editor to modify
/// Content of this method.
/// </Summary>
Private void InitializeComponent ()
{
This. Load + = new System. EventHandler (this. Page_Load );
}
# Endregion

Private string GenerateCheckCode ()
{
Int number;
String checkCode = String. Empty; // string for storing random Codes

System. Random random = new Random ();

For (int I = 0; I <4; I ++) // generates a four-digit Verification Code
{
Number = random. Next ();
Number = number % 36;
If (number <10)
{
Number + = 48; // The number 0-9 is encoded in 48-57
}
Else
{
Number + = 55; // The letter A-Z is encoded in 65-90
}

CheckCode + = (char) number). ToString ();
}

Response. Cookies. Add (new HttpCookie ("CheckCode", checkCode); // store random codes in Cookies

Return checkCode;
}

Private void CreateCheckCodeImage (string checkCode)
{
If (checkCode = null | checkCode. Trim () = String. Empty)
Return;

System. Drawing. Bitmap image = new System. Drawing. Bitmap (
(Int) Math. Ceiling (decimal) (checkCode. Length * 15), 20 );
// Create a Graphics object
Graphics g = Graphics. FromImage (image );

Try
{
// Generate a random Generator
Random random = new Random ();

// Clear the background color of the image
G. Clear (Color. White );

// 10 background noise lines
For (int I = 0; I <10; I ++)
{
// Noise line start coordinate (x1, y1), end coordinate (x2, y2)
Int x1 = random. Next (image. Width );
Int x2 = random. Next (image. Width );
Int y1 = random. Next (image. Height );
Int y2 = random. Next (image. Height );
// Draw the noise line with a silver line
G. DrawLine (new Pen (Color. Silver), x1, y1, x2, y2 );
}

// The font of the verification code in the output image: Arial on the 12th, bold and italic.
Font font = new System. Drawing. Font ("Arial", 12, (System. Drawing. FontStyle. Bold | System. Drawing. FontStyle. Italic ));
System. Drawing. Drawing2D. LinearGradientBrush brush = new System. Drawing. Drawing2D. LinearGradientBrush (
New Rectangle (0, 0, image. Width, image. Height ),
Color. Blue,
Color. DarkRed,
1.2f,
True );
G. DrawString (checkCode, font, brush, 2, 2 );

// Picture foreground noise: 50
For (int I = 0; I <50; I ++)
{
Int x = random. Next (image. Width );
Int y = random. Next (image. Height );

Image. SetPixel (x, y, Color. FromArgb (random. Next ()));
}

// Draw the border line of the image
G. DrawRectangle (
New Pen (Color. SaddleBrown ),
0,
0,
Image. Width-1,
Image. Height-1 );

// Create a memory stream for outputting Images
System. IO. MemoryStream MS = new System. IO. MemoryStream ();
Image. Save (MS, System. Drawing. Imaging. ImageFormat. Gif );
Response. ClearContent ();
Response. ContentType = "image/Gif ";
Response. BinaryWrite (ms. ToArray ());
}
Finally
{
G. Dispose ();
Image. Dispose ();
}
}

}

Next, add the HTML tag at the location where the verification code is used, set the "src" attribute to "RandomImage. aspx", and
Add the following verification code in the background:
Protected void button#click (object sender, EventArgs e)
{
// Check the verification code
If (Request. Cookies ["CheckCode"] = null)
{
Label2.Visible = true;
Label2.Text = "your system disables Cookies, so you cannot use the verification code ";
Return;
}
// Check whether the entered verification code is correct
If (string. Compare (Request. Cookies ["CheckCode"]. Value, TextBox6.Text, true )! = 0)
{
Label2.Text = "the verification code is incorrect. Enter the correct verification code! ";
Label2.Visible = true;
Return;
}
... // Omitted the data added to the database
}