static void Main(string[] args)
{
Student s1 = new Student("Artem", 20, 3);
s1.SetMarks();
int sum;
Console.WriteLine("average mark = " + s1.GetAvgMark(out sum));
Console.WriteLine("sum = " + sum);
string name;
int age;
s1.GetNameAge(out name, out age);
Console.WriteLine("name: " + name + " age: " + age);
Student s2 = new Student();
s1.CopyRef(ref s2);
s2.ShowInfo();
s2.SetNameAge(age: 21);
s2.SetMarkSubject("z", "z");
s2.SetMarkValue(0, 0, 0, 0, 0);
s2.SetNameAge(age: 25);
Student s3;
s2.CopyObj(out s3);
s3.ShowField(5);
}