public void AddGsmInTheList()
 {
     for (int i = 0; i < models.Length; i++)
     {
         GSM newGSM = new GSM(models[i], manufacturers[i], prices[i], owners[i]);
         GsmList.Add(newGSM);
     }
 }
        public void TestGSMCallHistory()
        {
            GSM gsm = new GSM("Note 2", "Samsung");

            gsm.AddCallInHistory(DateTime.Now.Date.ToShortDateString(), DateTime.Now.TimeOfDay, 0883123321, 15);
            gsm.AddCallInHistory(DateTime.Now.Date.ToShortDateString(), DateTime.Now.TimeOfDay + TimeSpan.FromHours(1), 0884123321, 43);
            gsm.AddCallInHistory(DateTime.Now.Date.ToShortDateString(), DateTime.Now.TimeOfDay + TimeSpan.FromHours(1.5), 0885123321, 250);

            gsm.PrintCallHistoryList();

            gsm.CalculatePriceOfAllCalls(0.37);

            gsm.DeleteLongestCall();

            gsm.PrintCallHistoryList();

            gsm.CalculatePriceOfAllCalls(0.37);
        }