private void button1_Click(object sender, EventArgs e)
 {
            SqlConnection con = new SqlConnection(); //create a SqlConnection class object
            con.ConnectionString = "Data Source=home-1117080bc2;Initial Catalog=Hotel_Booking;User  
            ID=sa;Password=sqlforarijit"; //create a connecting string
            con.Open(); //open the connection
            SqlCommand cmd = new SqlCommand("select * from new_reservation where customer_id = 
           @a", con);  //retrieve record(s) of customer from the database on the basis of id
            cmd.Parameters.Add("@a", SqlDbType.VarChar, 50); //add a parameter
            cmd.Parameters["@a"].Value = comboBox1.Text; //pass the parameter value from combobox
            SqlDataAdapter ada = new SqlDataAdapter(cmd); //create a SqlDataAdapter object and pass
                                                                                                         
                                                                                                         SqlCommand object as a parameter
            SqlCommandBuilder build = new SqlCommandBuilder(ada); // create a SqlCommandBuilder
                                                                                 
                                                                                 object and pass SqlDataAdapter object as a parameter
            DataSet ds = new DataSet(); //create a dataset
            ada.Fill(ds, "new_reservation"); //fill the data in a dataset, pass dataset object and virtual  
                                                         table name
                                                         table name
            dataGridView1.DataSource = ds.Tables[0]; // set dataset table as a datasource of datagridview
   }