private static void Add_Contract()
{
Console.WriteLine("Enter BabySitter ID:");
string babySitterID = Console.ReadLine();
Console.WriteLine("Enter Child ID:");
string ChildID = Console.ReadLine();
Console.WriteLine("first meeting has done? (y/n)");
bool firsMeating = yes_or_no(Convert.ToChar(Console.ReadLine()));
Console.WriteLine("which type of salary (y-hour rate/n-month rate)");
bool type = yes_or_no(Convert.ToChar(Console.ReadLine()));
Console.WriteLine("start day (xx/yy/zzzz)");
DateTime start = Convert.ToDateTime(Console.ReadLine());
Console.WriteLine("end day (xx/yy/zzzz)");
DateTime end = Convert.ToDateTime(Console.ReadLine());
BE.Contract con = new Contract(babySitterID, ChildID, firsMeating, type, start, end);
bl.addContract(con);
}