Class using Class

[ahmarajeel]

I have class called student that has lastname,firstname,credits,gpa,date of,birth,
matriculation date. I have another class called roster that has course name ,credits, instructor name, and it should contain a list of student from the student class .I created a list of student in roster . I am having problem with
constructors

how do I create a default constructor in roster.
here is my constructor:
Roster:: Roster(): course_name(""),
course_code(""),
credits(0),
instructor(""),
list("","",0,0.0,"",""),
count(0)
{
}