根据传智写的SqlHelper

 using System;
 using System.Configuration;
 using System.Data;
 using System.Data.SqlClient;

 namespace ADO连接数据库
 {
     public static class SqlHelper
     {
         //首先是连接字符串
         private static readonly string Strcon = ConfigurationManager.ConnectionStrings["mssqlserver"].ConnectionString;

         /// <summary>
         /// 增删改返回单条无内容ExcuteNonQuery方法
         /// </summary>
         /// <param name="sql">Sql执行语句</param>
         /// <param name="pms">传入变量</param>
         /// <returns></returns>
         public static int ExcuteNonQuery(string sql, params SqlParameter[] pms)
         {
             using (SqlConnection con = new SqlConnection(Strcon))
             {
                 using (SqlCommand cmd = new SqlCommand(sql, con))
                 {
                     if (pms != null)
                     {
                         cmd.Parameters.AddRange(pms);
                     }
                     con.Open();
                     return cmd.ExecuteNonQuery();
                 }
             }
         }

         /// <summary>
         /// 查询返回单条数据内容ExcuteScalar方法
         /// </summary>
         /// <param name="sql">Sql执行语句</param>
         /// <param name="pms">传入参数</param>
         /// <returns></returns>
         public static object ExcuteScalar(string sql, params SqlParameter[] pms)
         {
             using (SqlConnection con = new SqlConnection(Strcon))
             {
                 using (SqlCommand cmd = new SqlCommand(sql, con))
                 {
                     if (pms != null)
                     {
                         cmd.Parameters.AddRange(pms);
                     }
                     con.Open();
                     return cmd.ExecuteScalar();
                 }
             }
         }
         /// <summary>
         /// 查询Reader方法
         /// </summary>
         /// <param name="sql">Sql执行语句</param>
         /// <param name="pms">传入参数</param>
         /// <returns></returns>
         public static SqlDataReader Reader(string sql, params SqlParameter[] pms)
         {
             SqlConnection con = new SqlConnection(Strcon);
             using (SqlCommand cmd = new SqlCommand(sql, con))
             {
                 if (pms != null)
                 {
                     cmd.Parameters.AddRange(pms);
                 }
                 try
                 {
                     con.Open();
                     return cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
                 }
                 catch (Exception)
                 {
                     con.Close();
                     con.Dispose();
                     throw;
                 }
             }
         }
         /// <summary>
         /// DataTable方法
         /// </summary>
         /// <param name="sql">Sql执行语句</param>
         /// <param name="pms">可变Sql参数</param>
         /// <returns></returns>
         public static DataTable Adapter(string sql, params SqlParameter[] pms)
         {
             DataTable dt = new DataTable();
             using (SqlDataAdapter adapter = new SqlDataAdapter(sql, Strcon))
             {
                 if (pms != null)
                 {
                     adapter.SelectCommand.Parameters.AddRange(pms);
                 }
                 adapter.Fill(dt);
             }
             return dt;
         }
     }
 }

PS：需要引用一个配置文件

 <?xml version="1.0" encoding="utf-8" ?>
 <configuration>
   <connectionStrings>
     <add connectionString="Data Source=DESKTOP-B0QVA84;Catalog=MyfirstOne;Integrated Security=True" name="mssqlserver" />
   </connectionStrings>
 </configuration>