概述：輸錯三次禁止登陸，15分鐘後才能繼續。

圖示：

Form1程式碼：

using System;
using System.Configuration;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace 登入驗證專案
{
     public partial class Form1 : Form
     {
         public Form1()
         {
             InitializeComponent();
         }

        private void button1_Click(object sender, EventArgs e)
         {
             //連線資料庫
             //將連線字串寫入配置檔案中 string connStr = "sever=.;uid=sa;pwd=123456;database=demo";

這部分寫在配置檔案中

//<connectionStrings>
   // <add name="SqlConn" connectionString="server=.;uid=sa;pwd=123456;database=LoginBlock"/>
  //</connectionStrings>

             //條新增引用引入configuration名稱空間
             string connStr = ConfigurationManager.ConnectionStrings["SqlConn"].ConnectionString;
             using (SqlConnection conn = new SqlConnection(connStr))
             {
                 using (SqlCommand cmd = conn.CreateCommand())
                 {

                    conn.Open();
                     //select 查詢語句str
                     string str = @"SELECT  [Uid]
                                               ,[Unm]
                                               ,[Pwd]
                                               ,[ErrorDate]
                                               ,[ErrorTimes]
                                           FROM [Login_Block]
                                           WHERE Unm='" + textBox1.Text.Trim()
                                           + "' and Pwd='" + textBox2.Text.Trim() + "' ";
                     cmd.CommandText = str;
                     // bool ishasdata=false;

//這裡建立Login物件

                     Login login = null;
                     using (SqlDataReader reader = cmd.ExecuteReader())
                     {//判斷是否有資料
                         #region MyRegion
                         //if (!reader.hasrows)
                         //{
                         //    //修改錯誤時間，錯誤次數

                        //}
                         #endregion
                         #region MyRegion
                         if (reader.HasRows)
                         {
                             reader.Read();
                         }
                         #endregion
                         if (reader.Read())
                         {
                             login = new Login();
                             login.Uid = int.Parse(reader["Uid"].ToString());
                             login.Pwd = reader["Pwd"].ToString();
                             login.ErrorTimes = int.Parse(reader["ErrorTimes"].ToString());
                             login.Errordata = DateTime.Parse(reader["Errordate"].ToString());
                         }
                         // ishasdata = reader.HasRows;

                     }//花括號執行結束之前reader物件一直佔用conn物件
                     if (login == null/*!ishasdata*/)
                     {
                         //修改 錯誤時間，錯誤次數  where UserName=txtUserName.Text
                         cmd.CommandText =
                             "update Login_Block set Errordate=getdate(), ErrorTimes=ErrorTimes+1 where Unm='" +
                             textBox1.Text.Trim() + "'";
                         cmd.ExecuteNonQuery();
                         //MessageBox.Show("使用者名稱密碼Error");
                         return;
                     }
                     //執行有資料的過程
                     if (login.ErrorTimes < 3 || DateTime.Now.Subtract(login.Errordata).Minutes > 15)
                     {
                         MessageBox.Show("登入成功！！");
                         cmd.CommandText = "update Login_Block set ErrorTimes=0,Errordate=getdate() where Uid=" + login.Uid;
                         cmd.ExecuteNonQuery();
                     }
                     else
                     {
                         MessageBox.Show("登入失敗！賬號被鎖定");
                     }
                 }
             }
         }
     }
}

Login類：

using System;

namespace 登入驗證專案
{
     public class Login
     {
         //[Uid],[Pwd],[ErrorTimes],[Errordata]
         public int Uid { get; set; }
         public string Unm { get; set; }
         public string Pwd { get; set; }
         public int ErrorTimes { get; set; }
         public DateTime Errordata { get; set; }
     }
}

資料庫：

表：Login_Block

欄位：

[Uid]                                       

[Unm]                                       

[Pwd]                                      

[ErrorDate]                                           

[ErrorTimes]