系统管理（雏形）

 private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=Cml;user=sa;pwd=123");
            conn.Open();
            SqlCommand cmd = conn.CreateCommand();
            cmd.CommandText = "select * from yonghu where username='"+textBox1.Text+"' and userpass='"+textBox2.Text+"'";
            SqlDataReader dr =cmd.ExecuteReader();
            if (dr.Read())
            {
                erzhuye f = new erzhuye();
                this.Owner = f; //主窗体归副窗体所有,是为了关闭副窗体的时候，主窗体也一块被关闭
                this.Visible = false;//将主窗体隐藏掉
                f.WindowState = FormWindowState.Maximized;
                f.Show();
            }
            else
            {
                MessageBox.Show("登陆失败");
            }

        }

 private void 学生管理ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form1 f = new Form1(); //Form1为学生信息
            f.MdiParent = this; //将学生信息的父级设为副窗体的
            f.Show();
        }

       

        private void 教师管理ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Teacher f = new Teacher();  //teacher为教师信息
            f.MdiParent = this;//将教师信息的父级设为副窗体的
            f.Show();
        }

        private void 课程管理ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Course f = new Course(); //Course为课程信息
            f.MdiParent = this; //将课程信息的父级设为副窗体的
            f.Show();
        }

        private void 成绩管理ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Score f = new Score();//Score为成绩信息  
            f.MdiParent = this;//将成绩信息的父级设为副窗体的
            f.Show();
        }