VINIL.APP/proba/Form/SummaSaleDay.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 proba
{
    public partial class SummaSaleDay : Form
    {
        DataBase dataBase = new DataBase();
        public SummaSaleDay()
        {
            InitializeComponent();
        }

        private void button_back_Click(object sender, EventArgs e)
        {
            this.Hide();
            Form2 form2 = new Form2();
            form2.ShowDialog();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            dataBase.openConnection();
            double[] summa = new double[0];
            SqlCommand command = new SqlCommand($"SELECT summa From Sales WHERE date_sale = '{text_day.Text}'", dataBase.GetConnection());
            SqlDataReader reader = command.ExecuteReader();
            int i = 0;
            while (reader.Read())
            {
                Array.Resize(ref summa, summa.Length + 1);
                summa[i] = Convert.ToDouble(reader[0]);
                i++;
            }
            text_summa.Text = Convert.ToString(GetSumma(summa));
            text_summa.ForeColor = Color.Black;
            dataBase.closeConnection();
        }
        public static double GetSumma(double[] massive)
        {
            double summa = 0;
            for(int i = 0; i < massive.Length; i++)
            {
                summa += massive[i];
            }
            return summa;
        }
        private void text_day_Enter(object sender, EventArgs e)
        {
            if (text_day.ForeColor == Color.Gray)
            {
                text_day.Text = null;
                text_day.ForeColor = Color.Black;
            }
        }

        private void text_day_Leave(object sender, EventArgs e)
        {
            if(text_day.Text == "")
            {
                text_day.Text = "1 мая 2022";
                text_day.ForeColor = Color.Gray;
            }
        }
        private void SummaSaleDay_Load(object sender, EventArgs e)
        {
            text_day.Text = "1 мая 2022";
            text_day.ForeColor = Color.Gray;
            text_summa.Text = "Не редактируется";
            text_summa.ForeColor = Color.Gray;
        }
        public void global_FormClosed(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}