有时候在网页中登录时需要输入验证码,C#中也可以做到,以下是两种不同的方式：

第一种方式：

1. private void button1_Click(object sender, EventArgs e)
2. {
3. if (textBox3.Text != label4.Text) //验证码输入有误
4. {
5. MessageBox.Show("验证码输入错误！！！");
6. Random rnd = new Random();
7. //生成验证码
8. this.label4.Text = rnd.Next(1000, 9999).ToString(); //验证码取值范围
9. }
10. else
11. {
12. if (radioButton1.Checked) //管理员登录
13. {
14. if (textBox1.Text == "admin" && textBox2.Text == "admin")
15. {
16. Admin frm = new Admin();
17. frm.Show();
18. this.Hide();
19. }
20. else
21. {
22. MessageBox.Show("密码错误或者该用户不存在！！！");
23. textBox1.Text = "";
24. textBox2.Text = "";
25. textBox3.Text = "";
26. }
27. }
28. }
29. }

第二种方式：（推荐使用第一种,简单高效）

1. private void CreateVerificationCode(int CodeCount)
2. {
3. #region 产生验证码
4. string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,M,N,P,Q,R,S,T,U,W,X,Y,Z";
5. string[] allCharArray = allChar.Split(',');
6. string RandomCode = "";
7. int temp = -1;
8.  
9. Random rand = new Random();
10. for (int i = 0; i < CodeCount; i++)
11. {
12. if (temp != -1)
13. {
14. rand = new Random(temp * i * ((int)DateTime.Now.Ticks));
15. }
16.  
17. int t = rand.Next(33);
18.  
19. while (temp == t)
20. {
21. t = rand.Next(33);
22. }
23.  
24. temp = t;
25. RandomCode += allCharArray[t];
26. }
27. checkCode = RandomCode;
28.  
29. #endregion
30.  
31. #region 绘制验证码
32. int iwidth = (int)(checkCode.Length * 14);
33. System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 21);
34. Graphics g = Graphics.FromImage(image);
35. Font f = new System.Drawing.Font("Arial ", 10);//, System.Drawing.FontStyle.Bold);
36. Brush b = new System.Drawing.SolidBrush(Color.Black);
37. Brush r = new System.Drawing.SolidBrush(Color.FromArgb(166, 8, 8));
38.  
39. g.Clear(System.Drawing.ColorTranslator.FromHtml("#99C1CB"));//背景色
40.  
41. char[] ch = checkCode.ToCharArray();
42. for (int i = 0; i < ch.Length; i++)
43. {
44. if (ch[i] >= '0' && ch[i] <= '9')
45. {
46. //数字用红色显示
47. g.DrawString(ch[i].ToString(), f, r, 3 + (i * 12), 3);
48. }
49. else
50. { //字母用黑色显示
51. g.DrawString(ch[i].ToString(), f, b, 3 + (i * 12), 3);
52. }
53. }
54. System.IO.MemoryStream ms = new System.IO.MemoryStream();
55. image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
56. //history back 不重复
57. pictureBox1.Image = image;
58. #endregion
59.  
60. }

点击事件调用：

1. CreateVerificationCode(4); //4表示产生四位数验证码