static void Main(string[] args)
{
Student S1 = new Student("Jack", 20, "男");
S1.SetCredit(30);
Console.WriteLine("第一位學生");
S1.GetCredit();
Student S2 = new Student("Merry", 20, "女");
S2.SetCredit(40);
Console.WriteLine("第二位學生");
S2.GetCredit();
Console.WriteLine("第一位學生");
S1.GetCredit();
Console.Read();
}