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?

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();
}