C#連接SQL SERVER數據庫的登錄窗口

其中包含兩個文件：

1、App.config

<?XML version="1.0" encoding="utf-8" ?>
<configuration>
  <aPPSettings >
    <add key="url" value="192.168.0.2"/>
    <add key="database" value="WFXX"/>
    <add key="uname" value="sa"/>
    <add key="psd" value="sa"/>
  </aPPSettings >
</configuration>

2、Form1.cs 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClIEnt;

namespace Login
{
    public partial class Login : Form
    {
        string url = System.Configuration.ConfigurationSettings.APPSettings["url"];
        string database = System.Configuration.ConfigurationSettings.APPSettings["database"];
        string uname = System.Configuration.ConfigurationSettings.APPSettings["uname"];
        string psd = System.Configuration.ConfigurationSettings.APPSettings["psd"];

        public Login()
        {
            InitializeComponent();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string userlogin = txt_uname.Text;
            string psdlogin = txt_psd.Text;