请问验证码的随机字母+数字是怎么弄的?哪位知道请给个提示,谢谢.
下面是随机数字:
Bitmap img = new Bitmap(40,20);
Graphics g = Graphics.FromImage(img);
g.Clear(Color.Red);
Random rd = new Random();
string check = rd.Next(1000,9999).ToString();
Session.Add("ck",check);
g.DrawString(check,new Font("宋体",12,FontStyle.Bold),Brushes.Red,2,2);
img.Save(Response.OutputStream,System.Drawing.Imaging.ImageFormat.Gif);
Response.ContentType = "image/gif";
g.Dispose();
但是我想弄个随机字母加随机数字的而且是交叉显示的,该怎么弄?

小弟也想请教这个好久了，同盼大师指点

写个字符数组，比如char a[] = {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,1,2,3,4,5,6,7,8,9,0}
这样，你去第随机个值就可以了

public class ValidateCode : System.Web.UI.Page
{
private void Page_Load(object sender, System.EventArgs e)
{
this.CreateCheckCodeImage(GenerateCheckCode());
}

#region web 窗体设计器生成的代码
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: 该调用是 asp.NET web 窗体设计器所必需的。
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion

private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for(int i=0; i<5; i++)
{
number = random.Next();

if(number % 2 == 0)
code = (char)('0' + (char)(number % 10));
else
code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();
}

Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

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((checkCode.Length * 12.5)), 22);
Graphics g = Graphics.FromImage(image);

try
{
//生成随机生成器
Random random = new Random();

//清空图片背景色
g.Clear(Color.White);

//画图片的背景噪音线
for(int i=0; i<25; i++)
{
int x1 = random.Next(image.Width);
int x2 = random.Next(image.Width);
int y1 = random.Next(image.Height);
int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
}

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);

//画图片的前景噪音点
for(int i=0; i<100; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);

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

//画图片的边框线
g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

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();
}
}
}

我做了个简单的.
private string GenCode(int num)
{
string[]source={"2","3","4","5","6","7","8","9","a","b","c","d","e","f","g","h","i","j","k","m","n","p","q","r","s","t","u","v","w","x","y","z"};
string code="";
Random rd=new Random();
for(int i=0;i<num;i++)
{
code += source[rd.Next(0,source.Length)];
}

return code;
}

//生成图片
private void GenImg()
{
string code = this.GenCode(4);
Bitmap img=new Bitmap(45,20);//定义一个画板

Graphics gh=Graphics.FromImage(img);//在画板上定义绘图的实例
gh.Clear(Color.White);
gh.DrawString(code,new Font("宋体",13,FontStyle.Regular),Brushes.Red,2,2);

img.Save(Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);//将图片显示出来

Session.Add("ValidateCode",code);//将字符串保存到Session中，以便需要时进行验证

gh.Dispose();
img.Dispose();
}

各位大哥厉害啊，加我QQ273085302，请今后指点小弟。