利用C#编写学员信息管理系统

新手写一段学员信息管理系统，有代码冗余的情况请谅解，代码如下，请大神指点

//登陆入口页面
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 学员管理系统
{
    public partial class Lo : Form
    {
        public Lo()
        {
            InitializeComponent();
        }
         string sql= "Data Source=LAPTOP-PCMBBB0N;Initial Catalog=DB_Student;Trusted_Connection=true;";
          private void Log_Load(object sender, EventArgs e)
        {
            this.FormBorderStyle = FormBorderStyle.FixedToolWindow;
            this.Location = new Point(Screen.PrimaryScreen.Bounds.Width / 2 - this.Width / 2, Screen.PrimaryScreen.Bounds.Height / 2 - this.Height / 2);
        }
        Main main;
         private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                string  pwd =txtpwd.Text;
                if (pwd.ToString() == "")
                {
                    label2.Visible = true;
                    label2.Text = "密码不能为空！";
                }
                else
                {
                    if (pwd.Equals((table.Rows[0]["Pwd"]).ToString()))
                    {
                        label2.Visible = false;
                        main = new Main();
                        main.Show();
                        this.Visible = false;
                    }
                    else
                    {
                        label2.Text = "密码不正确！";
                        label2.Visible = true;
                    }
                }
            }
            catch (Exception)
            {
                throw;
            }
        }
        DataTable table = new DataTable();
        private void txtid_Leave(object sender, EventArgs e)
        {
            try
            {
                int id = int.Parse(txtid.Text);
                 //1.链接数据库对象
                  SqlConnection sqlcon = new SqlConnection(sql);
                //3.创建数据库命令对象
                SqlCommand cmd = new SqlCommand();
                cmd.Connection = sqlcon;
                 cmd.CommandText = "SELECT * FROM Student WHERE ID=" + id;
                 //5.数据适配器对象
                SqlDataAdapter sda = new SqlDataAdapter();
                sda.SelectCommand = cmd;
                //6.这个table可以用来接受适配的最终结果
                sda.Fill(table);
                 if (table.Rows.Count > 0)
                {
                    label1.Visible = false;
                }
                else
                {
                    label1.Visible = true;
                    label1.Text = "输入ID不存在！";
                }
            }
            catch (Exception)
            {
               
                label1.Visible = true;
                label1.Text = "请输入纯数字ID！";
                txtid.Focus();
                txtid.Text = "";
            }
        }
        private void button2_Click_1(object sender, EventArgs e)
        {
            Register register = new Register();
            register.ShowDialog();
            this.Visible = true;
            label1.Visible = false;
        }
    }
}

//注册页面
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace 学员管理系统
{
    public partial class Register : Form
    {
        public Register()
        {
            InitializeComponent();
        }
        string sql = "Data Source=LAPTOP-PCMBBB0N;Initial Catalog=DB_Student;Trusted_Connection=true;";
         private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                SqlConnection sqlCon = new SqlConnection(sql);
                string sqltxt = string.Format("INSERT INTO Student VALUES('{0}','{1}','{2}','{3}','{4}')", textBox2.Text, textBox1.Text, textBox3.Text, textBox4.Text, textBox5.Text);
                SqlCommand cmd = new SqlCommand(sqltxt, sqlCon);
                sqlCon.Open();
                int res = cmd.ExecuteNonQuery();
                if (res > 0)
                {
                    MessageBox.Show("注册成功");
                    textBox1.Text = "";
                    textBox2.Text = "";
                    textBox3.Text = "";
                    textBox4.Text = "";
                    textBox5.Text = "";
                    textBox1.Focus();
                }
            }
            catch (Exception)
            {
                throw;
            }
        }
        

//信息页面（可以进行数据库信息更改，删除，查看 以及翻页操作）
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace 学员管理系统
{
    public partial class Main : Form
    {
        public Main()
        {
            InitializeComponent();
        }     
         string strcon = "Data Source=LAPTOP-PCMBBB0N;Initial Catalog=DB_Student;Trusted_Connection=true;";
        int countPage;
        int nowPage = 1;
        SqlConnection sqlCon;
          private void Main_Load(object sender, EventArgs e)
        {
            sqlCon = new SqlConnection(strcon);
            //绑定页码信息
            try
            {
                string sql = "SELECT COUNT(*) FROM Student";
                SqlCommand cmdl = new SqlCommand(sql, sqlCon);
                sqlCon.Open();
                object res = cmdl.ExecuteScalar();
                if (res != null)
                {
                    if ((int)res % 6 > 0)
                    {
                        countPage = ((int)res / 6) + 1;
                    }
                    else
                    {
                        countPage = (int)res / 6;
                    }
                }
            }
            catch (Exception)
            {
                throw;
            }
            finally
            {
                sqlCon.Close();
            }
            //初始信息绑定
            try
            {
                SetPage(sqlCon);
                dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
                dataGridView1.RowHeadersVisible = false;
                foreach (DataGridViewColumn dc in dataGridView1.Columns)
                {
                    dc.SortMode = DataGridViewColumnSortMode.Programmatic;
                }
                dataGridView1.ColumnHeadersDefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
                dataGridView1.DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
                dataGridView1.ScrollBars = ScrollBars.None;
                dataGridView1.MultiSelect = false;
                dataGridView1.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
                dataGridView1.AllowUserToResizeRows = false;
                dataGridView1.AllowUserToResizeColumns = false;                      
                dataGridView1.ScrollBars = ScrollBars.None;
                dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
                dataGridView1.AllowUserToAddRows = false;
                dataGridView1.DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
                dataGridView1.ColumnHeadersDefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
                foreach (DataGridViewColumn item in dataGridView1.Columns)
                {
                    item.SortMode = DataGridViewColumnSortMode.NotSortable;
                }
                dataGridView1.ReadOnly = true;
                dataGridView1.CellMouseDown += DataGridView1_CellMouseDown;
            }
            catch (Exception ex)
            {
                throw;
            }
            finally
            {
                sqlCon.Close();
            }
        }
        private void SetPage(SqlConnection sqlCon)
        {
            string sql = string.Format("SELECT ID AS '账号',NAME AS '姓名',Sex AS '性别',Age AS '年龄',Zhanli AS '电话' FROM Student WHERE ID IN(SELECT TOP(6) ID FROM Student WHERE ID NOT IN (SELECT TOP({0}) ID FROM Student ORDER BY ID)ORDER BY ID ) ORDER BY ID", (nowPage - 1) * 6);
            SqlCommand cmd = new SqlCommand(sql, sqlCon);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];
            label1.Text = nowPage.ToString();
            label3.Text = countPage.ToString();
        }
         private void DataGridView1_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right && dataGridView1.SelectedRows.Count > 0)
            {
                dataGridView1.ClearSelection();
                dataGridView1.Rows[e.RowIndex].Selected = true;
                ID.Idd = (int)dataGridView1.SelectedCells[0].Value;
                contextMenuStrip1.Show();
            }
        }
        private void 删除ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
            try
            {
                SqlConnection sqlCon = new SqlConnection(strcon);
                string sqltxt = "DELETE FROM Student WHERE ID=" + ID.Idd;
                SqlCommand cmd = new SqlCommand(sqltxt, sqlCon);
                sqlCon.Open();
                int res = cmd.ExecuteNonQuery();
                if (res > 0)
                {
                    MessageBox.Show("删除成功！");
                    Main ma = new 学员管理系统.Main();
                    ma.Show();
                    this.Visible = false;
                }
            }
             catch (Exception)
            {
                throw;
            }
        }
        private void 修改密码ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            xiugai xiu = new xiugai();
            xiu.ShowDialog();
            this.Visible = false;
        }
        private void 查看详细信息ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            chakan cha = new chakan();
            cha.ShowDialog();
            this.Visible = false;
        }
        private void 下一页ToolStripMenuItem_Click(object sender, EventArgs e)
        {
          
            if (nowPage >= countPage)
            {
                return;
            }
            else
            {
                nowPage++;
                SetPage(sqlCon);
            }
        }
         private void 上一页ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (nowPage <= 1)
            {
                return;
            }
            else
            {
                nowPage--;
                SetPage(sqlCon);
            }
        }
    }
}

/查看详细信息
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 学员管理系统
{
    public partial class chakan : Form
    {
        public chakan()
        {
            InitializeComponent();
        }
         private void button1_Click(object sender, EventArgs e)
        {
            Main ma = new 学员管理系统.Main();
            ma.Show();
            this.Visible = false; 
        }
        string sql = "Data Source=LAPTOP-PCMBBB0N;Initial Catalog=DB_Student;Trusted_Connection=true;";
        private void chakan_Load(object sender, EventArgs e)
        {
            try
            {
                SqlConnection sqlcon = new SqlConnection(sql);
                string sqltxt = "SELECT * FROM Student WHERE ID="+ID.Idd;  
                SqlCommand cmd = new SqlCommand(sqltxt, sqlcon);
                sqlcon.Open();
                SqlDataAdapter sda = new SqlDataAdapter(cmd);
                DataTable table = new DataTable();
                sda.Fill(table);
                Name1.Text = (table.Rows[0]["NAME"]).ToString();
                ID1.Text = (table.Rows[0]["ID"]).ToString();
                Pwd.Text = (table.Rows[0]["Pwd"]).ToString();
                Sex.Text = (table.Rows[0]["Sex"]).ToString();
                Age.Text = (table.Rows[0]["Age"]).ToString();
                Zhanli.Text = (table.Rows[0]["Zhanli"]).ToString();
            }
            catch (Exception)
            {
          	  throw;
            }
        }
    }
}

//创建一个类用来存储用户账号
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 学员管理系统
{
    public  class ID
    {
        public  static int idd;
        public static int Idd
        {
            get
            {
                return idd;
            }
            set
            {
                idd = value;
            }
        }
    }
}

//修改密码
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace 学员管理系统
{
    public partial class xiugai : Form
    {
        public xiugai()
        {
            InitializeComponent();
        }
        string sql = "Data Source=LAPTOP-PCMBBB0N;Initial Catalog=DB_Student;Trusted_Connection=true;";
        private void button1_Click(object sender, EventArgs e)
        {
            string yuan = textBox1.Text;
            string New = textBox2.Text;
            string New2 = textBox3.Text;
            if (yuan=="")
            {
                label4.Visible = true;
                textBox1.Focus();
            }
            else
            {
                if (New=="")
                {
                    label5.Visible = true;
                    textBox2.Focus();
                }
                else
                {
                    if (New2==""||New2!=New)
                    {
                        label6.Visible = true;
                        textBox3.Focus();
                    }
                    else
                    {
                        try
                        {
                            int num = int.Parse(yuan);
                            SqlConnection sqlcon = new SqlConnection(sql);
                            string sqltext = "UPDATE Student SET Pwd=" + New2 + "WHERE ID="+ID.Idd;
                            //string sqltext = "UPDATE StudentInfor SET Pwd=" + New2 + "WHERE ID="+ID.Idd;
                            SqlCommand cmd = new SqlCommand(sqltext,sqlcon);
                            sqlcon.Open();
                            int res = cmd.ExecuteNonQuery();
                            if (res>0)
                            {
                                MessageBox.Show("修改成功");
                            }
                        }
                        catch (Exception)
                        {
                            throw;
                        }
                    }
                }
            }
        }
    }
}