public string Carica(string campo_1, string campo_2, string campo_3)
    {
        string campo_4 = "0";
        SqlConnection conn = new SqlConnection();
        SqlCommand com = new SqlCommand();
        conn.ConnectionString = "Data Source=***\\SQLEXPRESS;Initial Catalog=***;Integrated Security=True";
        com.Connection = conn;
        com.CommandText = "SELECT * FROM Timesheet WHERE ID_Dipendente = '" + campo_1 + "' and Data_Timesheet = '" + campo_2 + "' and ID_Commessa = '" + campo_3 + "'";
        conn.Open();
        SqlDataAdapter DA = new SqlDataAdapter();
        DataSet DS = new DataSet();
        DA.SelectCommand = com;
        DA.Fill(DS, "TAB");
        conn.Close();
        if (DS.Tables["TAB"].Rows.Count > 0)
        {
            foreach (DataRow riga in DS.Tables["TAB"].Rows)
            {
                campo_4 = riga["Ore"].ToString();
            }
        }
        return campo_4;
    }