how to struct initializer and deque - c++

Question

So i have..
struct Polynomial{
deque<long> coefs;
long degree;
Polynomial(initializer_list<long> co_list);
Polynomial(deque<long> & co_list);
Polynomial();
string poly_to_string();
Polynomial add(Polynomial rhs);
Polynomial mult(Polynomial rhs);
Polynomial mult(long factor);
}
For theese methods I have to :
Polynomial(initializer_list cfs ). Initialize the instance using an initializer list of coefficients.
-order is the highest power goes first, lowest last
-coefs and degree updated.
Polynomial(deque cfs). Initialize the instance using a vector of coefficients. -order is the highest power goes first, lowest last
-coefs and degree updated.
Then I do methods to add/multiple/factor the polynomial, which I can do, just not sure what
Polynomial(initializer_list<long> co_list);
Polynomial(deque<long> & co_list);
are suppose to do / how to start them..
Also, how would i would I start the function to return
Polynomial.degree
To return a long value?

Answer 1

Those two functions are the constructors for the type. They tell the compiler how to set up a Polynomial object so that it's ready for members to be called. They're most easily understood like this:
struct Polynomial{
deque<long> coefs;
long degree;
Polynomial(initializer_list<long> co_list);
Polynomial(deque<long> & co_list);
};
Polynomial::Polynomial(initializer_list<long> co_list)
{
//at this point, the members are created, but have no values
//so we assign values to the members
coefs.assign(co_list.begin(), co_list.end());
degree = co_list.size();
}
int main()
{
Polynomial mypoly = {3, 4, 5};
//creates a Polynomial variable from an initializer list
//the compiler runs the constructor function automatically
//so now it's members are all properly set, and we can run other functions
mypoly.do_thing();
}
However, as shown above, the Polynomial constructor constructs the two members, and then executes the function that assigns them values. We can make this even better by constructing them directly with the intended values:
Polynomial::Polynomial(initializer_list<long> co_list)
:
coefs(co_list.begin(), co_list.end()), //constructed directly
degree(co_list.size())
{
//they already have the needed values, don't need to do anything more
//to finalize the construction
}