public static string GetPhoneNumberFromUser() { string phoneNumStr = null; bool inputIsValid = false; while (inputIsValid == false) { Console.WriteLine("Please enter your phone number"); phoneNumStr = Console.ReadLine(); inputIsValid = ClientCard.IsPhoneNumberValid(phoneNumStr); if (inputIsValid == false) { Console.WriteLine("The number must contain 10 digits"); } } return(phoneNumStr); }