程序代码：

namespace 练习5
{
    public partial class Form1 : Form
    {
        private int cishu = 0;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string name = textBox1.Text;
            string pass = textBox2.Text;
           //admin不区分大小写！ name.Equals("admin",StringComparison.OrdinalIgnoreCase)
            if (name.Equals("admin", StringComparison.OrdinalIgnoreCase) && pass == "8888")
            {
                MessageBox.Show("恭喜你,登录成功");

               
            }
            else
            {
                cishu++;//cishu要做成private int cishu; 局部变量是没有用的！
                if (cishu > 3)

                {
                    MessageBox.Show("错误次数过多，程序结束");
                   
                    Application.Exit();//关闭程序代码 用this.close();也可以
                }
                MessageBox.Show("你输入的信息不正确,登录失败.");
            }

 
        }

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

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }
    }
}