linked lists problem (T/F verification)

[Soko]

Hello. Not sure if this belongs in the beginner's forum or not, but thought I would put it here to start.

So, I made a linked list to represent a polynomial:

struct nodeType
{
double coeff; //coefficiect
int pow; // power
nodeType *link;
}; // end nodeType 

And then made a class to represent the polynomial (making it, editing it, etc.):

class poly
{
private:
        nodeType *head;
public:
        poly(); //Default Constructor
        //This will set head to NULL;

        poly(double, int, nodeType *);//Copy Constructor
        //This will set the double to coefficient, the int to power, and the pointer to link

        ~poly(); //Destructor
        //This will deallocate all memory created with this program

        int degree();
        //This function returns the degree of the polynomial

        double coefficient(int);
        //This function returns the coefficient of the power input

        void changeofcoefficient(double, int);
        //This function finds the list member with the specified power and changes the coeffient

        nodeType* mult(double);
        //This function multiplies the polynomial by a constant, then returns the polynomial

        void print();
        //This function prints the polynomial
};

In my changeofcoefficient function (which is the only one you can edit the polynomials with...

void poly:: changeofcoefficient(double newcoeff, int power)
{
        nodeType *cur, *prev;

        if (head == NULL)
        {
                head = new nodeType;
                head->coeff = newcoeff;
                head->pow = power;
                head->link = NULL;
        }
        else
        {
                int n=0;
bool testcase = true;
                cur = head;
                prev = cur;
if (head->link == NULL)
cout << "Head's link is NULL" << endl;
else
cout << "Head's link is not NULL" << endl;


if (cur->link == NULL)
cout << "Current's link is NULL" << endl;
else
cout << "Current's link is not NULL" << endl;

if (cur->link != NULL)
cout << "Current's link is NOT NULL" << endl;

//Very confused.  When tested, cur->link is null, yet it still enters loop, causing cur->power to be NULL, causing a core dump.
//Also, head is always == NULL, not sure why.  And when head == NULL, skips over if (head == NULL) statement, and continues.
//So in this case, this is a very confusing case when true =/= true and false =/= false.


                while ((cur->link != NULL) || (cur->pow > power));      //CORE DUMP HAPPENS HERE
//              do
                {

                        cout << "FLAG" <<++n<< endl;
                        prev = cur;
                        cout << "FLAG" <<++n<< endl;
                        cur = cur->link;
                        cout << "FLAG" <<++n<< endl;
/*
testcase = (testcase && (cur->pow > power));
cout << "FLAG9" << endl;

testcase = (testcase && (cur->link != NULL));
cout << "FLAG10" << endl;
*/
                }
//              while (testcase);
//              while ((cur->pow > power) && (cur->link != NULL));      //CORE DUMP HAPPENS HERE
cout << "FLAG11" << endl;
                if (cur->pow == power)
                if (cur->pow == power)
                {
cout << "CHANGING EXISTING COEF" << endl;
                        cur->coeff = newcoeff;
                }

cout << "FLAG12" << endl;

etc.

My core dump happens here: when I compile and run, I get this:
What would you like in your polynomial? Please enter in the coefficient.
2
Please enter in the power.
2
Would you like to add elements to the current polynomial?
y
What would you like in your polynomial? Please enter in the coefficient.
3
Please enter in the power.
3
Head's link is NULL
Current's link is NULL
FLAG1
FLAG2
FLAG3
FLAG11
Segmentation fault (core dumped)


--------------------------------------------------------------------
Problems: Even when the while loop is false, it inters it anyway.
Even if head == NULL as shown by the cout statement, it foregoes the if statement on top.
Then obviously the coredump.

Another note: This function is called twice, once when head is actually null, and it works fine, the other time when head is not null (adding a secnod element to the polynomial) yet it reports head is null and core dumps that time.

If you need more code, let me know.

And this is a class project, but it was already due today, now just trying to learn from it :)