Datagridview Windows Form Edit

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace Insert_Update_Delete_DataGridView
{
    public partial class Form1 : Form
    {
        string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["dsn"];
        OleDbCommand com;
        OleDbDataAdapter oledbda;
        string str;
        DataSet ds;
  
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            bindgrid();
        }
        private void bindgrid()
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            con.Open();
            str = "select * from employee";
            com = new OleDbCommand(str, con);
            oledbda = new OleDbDataAdapter(com);
            ds = new DataSet();
            oledbda.Fill(ds, "employee");
            dataGridView1.DataMember="employee";
            dataGridView1.DataSource = ds;
            con.Close();
        }
        private void Clear()
        {
            txt_sno.Text = "";
            txt_name.Text = "";
            txt_address.Text = "";
            txt_age.Text = "";
        }

        private void btn_edit_Click(object sender, EventArgs e)
        {
            int i;
            i = dataGridView1.SelectedCells[0].RowIndex;
            txt_sno.Text = dataGridView1.Rows[i].Cells[1].Value.ToString();
            txt_name.Text = dataGridView1.Rows[i].Cells[2].Value.ToString();
            txt_address.Text = dataGridView1.Rows[i].Cells[3].Value.ToString();
            txt_age.Text = dataGridView1.Rows[i].Cells[4].Value.ToString();
        }

        private void btn_update_Click(object sender, EventArgs e)
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            con.Open();
            str = "Update employee set sno=@sno,name=@name,address=@address,age=@age Where sno=@sno";
            com = new OleDbCommand(str, con);
            com.Parameters.AddWithValue("@sno", txt_sno.Text);
            com.Parameters.AddWithValue("@name", txt_name.Text);
            com.Parameters.AddWithValue("@address", txt_address.Text);
            com.Parameters.AddWithValue("@age", txt_age.Text);
            com.ExecuteNonQuery();
            MessageBox.Show("Record Successfully Updated");
            con.Close();
            bindgrid();
            Clear();
        }

        private void btn_delete_Click(object sender, EventArgs e)
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            com = new OleDbCommand();
            if (dataGridView1.Rows.Count > 1 && dataGridView1.SelectedRows[0].Index != dataGridView1.Rows.Count - 1)
            {
                com.CommandText = "DELETE FROM employee WHERE ID=" + dataGridView1.SelectedRows[0].Cells[0].Value.ToString() + "";
                con.Open();
                com.Connection = con;
                com.ExecuteNonQuery();
                con.Close();
                dataGridView1.Rows.RemoveAt(dataGridView1.SelectedRows[0].Index);
                MessageBox.Show("Record Successfully Deleted");
            }
            bindgrid();
        }

        private void btn_insert_Click(object sender, EventArgs e)
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            con.Open();
            str = "Insert into employee(sno,name,address,age) Values (@sno,@name,@address,@age)";
            com = new OleDbCommand(str, con);
            com.Parameters.AddWithValue("@sno", txt_sno.Text);
            com.Parameters.AddWithValue("@name", txt_name.Text);
            com.Parameters.AddWithValue("@address", txt_address.Text);
            com.Parameters.AddWithValue("@age", txt_age.Text);
            com.ExecuteNonQuery();
            con.Close();
            MessageBox.Show("Record Successfully Inserted");
            bindgrid();
            Clear();
        }
    }
}