Project/project/DannyeAdd.cs

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 project
{
    public partial class DannyeAdd : Form
    {

        DataBase dataBase = new DataBase();
        public DannyeAdd()
        {
            InitializeComponent();
        }

        private void button4_Click(object sender, EventArgs e)
        {
            dataBase.openConnection();
            var addQuery = $"insert into Dannye (name_dan, adres_dan, city_dan, number_dan, contact_dan) values ('{textBox1.Text}','{textBox2.Text}','{textBox3.Text}','{textBox4.Text}','{textBox5.Text}')";
            var command = new SqlCommand(addQuery, dataBase.GetConnection());
            command.ExecuteNonQuery();
            MessageBox.Show("Запись успешно добавлена в таблицу");
            dataBase.closeConnection();
            this.Hide();
            Main MAIN = new Main();
            MAIN.Show();
        }

        private void DannyeAdd_FormClosed(object sender, FormClosedEventArgs e)
        {
            Application.Exit();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Hide();
            Main main = new Main();
            main.Show();
        }
    }
}