Multiplying Polynomials using recursion

I am using the GNU Compiler.

I am trying to multiply 2 polynomials.

Using recursion and arrays. Polynom.cpp has already been completed by the instructor. We just need to finish main.cpp, specifically (void MultPoly (Polynomial p, Polynomial q, Polynomial& r).)

The following the block is what is giving me issues:

void MultPoly (Polynomial p, Polynomial q, Polynomial& r)
{
    int deg;
    float coEff;

    deg=p.GetDegree();
    coEff=p.GetCoefficient(deg);
    p.DeleteTerm(deg);
    MultPoly(p,q,r);
    coEff=coEff*r.GetCoefficient(deg);
    r.InsertTerm(coEff,deg);
}

The whole program compiles correctly, but I am not getting any result for multiplying polynomials when I input 2 of them. It doesn't seg fault, it just doesn't print anything.

All it needs to do is multiply 2 polynomials together, then print the result to the screen.

Thanks for the help!
jonisgoneAsked:
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BlackDiamondConnect With a Mentor Commented:
Jon,
Here is the solution to your problem.  You were close, but needed a non-destructive ADD function.  That got rid of the need to use the insert in the mult function (you just call mult and add recursively).

cheers, BD

void AddPoly (Polynomial p, Polynomial q, Polynomial& r)

// Precondition: p and q are polynomials.
//
// Postcondition: r is the sum of p and q.
//
// Uses recursion.

{
    int deg;
    float coEff;
    Polynomial p_copy, q_copy;
//  Make sure r is zeroed out.  This is useful for Mult.
    while (!r.IsZero()) {
     r.DeleteTerm(r.GetDegree());
    }
    if (p.IsZero())
     r.CopyFrom(q);
    else
    {
//  Make safe copies of p and q
     p_copy.CopyFrom(p);
     q_copy.CopyFrom(q);
     deg=p_copy.GetDegree();
     coEff=p_copy.GetCoefficient(deg);
     p_copy.DeleteTerm(deg);
     AddPoly(p_copy,q_copy,r);
     coEff=coEff+r.GetCoefficient(deg);
     r.InsertTerm(coEff,deg);
    }

}

void MultPoly (Polynomial p, Polynomial q, Polynomial& r)
{
    int deg;
    float coEff;
    Polynomial q_copy, multresult, addresult;
    if(! p.IsZero()) {

       deg=p.GetDegree();
       coEff=p.GetCoefficient(deg);
       p.DeleteTerm(deg);
       MultPoly(p,q,r);
       q_copy.CopyFrom(q);
       EasyMult(coEff,deg,q_copy,multresult);
       AddPoly(multresult,r,r);
    }
}

void EasyMult (float a, int m, Polynomial p, Polynomial &multresult)
{
     int deg;
     float coEff;
     if (! p.IsZero()) {
        deg=p.GetDegree();
        coEff=p.GetCoefficient(deg);
        p.DeleteTerm(deg);
        EasyMult(a, m, p, multresult);
        deg = deg + m;
        coEff = coEff * a;
        multresult.InsertTerm(coEff,deg);
     }
}

 
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thienpnguyenCommented:
You use "recursive algorithm" but I don't see the algorithm's base case : when the algorithm stops to call itseft .

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thienpnguyenCommented:
Could you explain what DeleteInsert and InsertTerm( coEff, deg) does ?
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BlackDiamondCommented:
if (deg > 0){
   MultPoly(p,q,r);
}
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thienpnguyenCommented:
Not only that bug, I think that the algorithm also has problem . But I don't know what DeleteItem and InsertItem, I can not point out exactly what problem is
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jonisgoneAuthor Commented:
DeleteTerm allows for the next term in the Polynomial p to be examined(that was input by the user at the beginning of the program).  

InsertTerm will be what is printed out to the screen at the end of the program.  It is not part of main.cpp but poly.cpp...it looks like this:

void Polynomial::InsertTerm (float coeff, int deg)

// Precondition:
//     A nonnegative degree deg and a coefficient coeff are assigned
// Postcondition:
//     The polynomial contains a term of degree deg whose coefficient
//     is coeff.  If the polynomial originally had a term of degree deg
//     then the coefficient of that term has been replaced.  If coeff
//     is zero the result is the same as DeleteTerm (deg).

{
    if ( fabs(coeff) < .000001 )
    {
      DeleteTerm (deg);
      return;
    }

    Term* currPtr;       // Moving pointer
    Term* prevPtr;       // Pointer to node before *currPtr

// Find previous insertion point

    prevPtr = NULL;
    currPtr = leadingTerm;
    while (currPtr != NULL && deg < currPtr->degree)
    {
        prevPtr = currPtr;
        currPtr = currPtr->link;
    }

// Replace coefficient, if appropriate.

    if (currPtr != NULL && deg == currPtr->degree)
    {
      currPtr->coefficient = coeff;
      return;
    }

// Set up node to be inserted

    Term* newTerm = new Term;
    newTerm->degree = deg;
    newTerm->coefficient = coeff;

// Insert new term

    newTerm->link = currPtr;
    if (prevPtr == NULL)
        leadingTerm = newTerm;
    else
        prevPtr->link = newTerm;
};

//******************************************************************

void Polynomial::DeleteTerm (int deg)

// Precondition:
//     an integer deg is assigned
// Postcondition:
//     The term of degree deg in the polynomial (if it existed) has been
//     removed

{
    Term* delPtr;     // Pointer to term to be deleted
    Term* currPtr;    // Loop control pointer

// Do nothing if the polynomial is zero

    if (leadingTerm == NULL)
        ;

// Check if term to be deleted is first term

    else if (deg == leadingTerm->degree)
    {
        delPtr = leadingTerm;
        leadingTerm = leadingTerm->link;
        delete delPtr;
    }

// Search for node in rest of list

    else
    {
        currPtr = leadingTerm;
        while (currPtr->link != NULL && currPtr->link->degree > deg)
            currPtr = currPtr->link;
        if (currPtr->link != NULL && currPtr->link->degree == deg)
        {
            delPtr = currPtr->link;
            currPtr->link = currPtr->link->link;
            delete delPtr;
        }
    }
};
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jonisgoneAuthor Commented:
DeleteTerm allows for the next term in the Polynomial p to be examined(that was input by the user at the beginning of the program).  

InsertTerm will be what is printed out to the screen at the end of the program.  It is not part of main.cpp but poly.cpp...it looks like this:

void Polynomial::InsertTerm (float coeff, int deg)

// Precondition:
//     A nonnegative degree deg and a coefficient coeff are assigned
// Postcondition:
//     The polynomial contains a term of degree deg whose coefficient
//     is coeff.  If the polynomial originally had a term of degree deg
//     then the coefficient of that term has been replaced.  If coeff
//     is zero the result is the same as DeleteTerm (deg).

{
    if ( fabs(coeff) < .000001 )
    {
      DeleteTerm (deg);
      return;
    }

    Term* currPtr;       // Moving pointer
    Term* prevPtr;       // Pointer to node before *currPtr

// Find previous insertion point

    prevPtr = NULL;
    currPtr = leadingTerm;
    while (currPtr != NULL && deg < currPtr->degree)
    {
        prevPtr = currPtr;
        currPtr = currPtr->link;
    }

// Replace coefficient, if appropriate.

    if (currPtr != NULL && deg == currPtr->degree)
    {
      currPtr->coefficient = coeff;
      return;
    }

// Set up node to be inserted

    Term* newTerm = new Term;
    newTerm->degree = deg;
    newTerm->coefficient = coeff;

// Insert new term

    newTerm->link = currPtr;
    if (prevPtr == NULL)
        leadingTerm = newTerm;
    else
        prevPtr->link = newTerm;
};

//******************************************************************

void Polynomial::DeleteTerm (int deg)

// Precondition:
//     an integer deg is assigned
// Postcondition:
//     The term of degree deg in the polynomial (if it existed) has been
//     removed

{
    Term* delPtr;     // Pointer to term to be deleted
    Term* currPtr;    // Loop control pointer

// Do nothing if the polynomial is zero

    if (leadingTerm == NULL)
        ;

// Check if term to be deleted is first term

    else if (deg == leadingTerm->degree)
    {
        delPtr = leadingTerm;
        leadingTerm = leadingTerm->link;
        delete delPtr;
    }

// Search for node in rest of list

    else
    {
        currPtr = leadingTerm;
        while (currPtr->link != NULL && currPtr->link->degree > deg)
            currPtr = currPtr->link;
        if (currPtr->link != NULL && currPtr->link->degree == deg)
        {
            delPtr = currPtr->link;
            currPtr->link = currPtr->link->link;
            delete delPtr;
        }
    }
};
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jonisgoneAuthor Commented:
I did a little more work on the function, and came up with this.  I am including AddPoly in hopes someone will understand more clearly what I am asking (keep getting seg fault for product of the Polys):

void MultPoly (Polynomial p, Polynomial q, Polynomial& r)
{
    int deg;
    float coEff;

    deg=p.GetDegree();
    coEff=p.GetCoefficient(deg);
    p.DeleteTerm(deg);
    MultPoly(p,q,r);
    EasyMult(coEff,deg,q);   //multiplies leading term by rest
    AddPoly(p,q,r);          //will addup p & q polys
    r.InsertTerm(coEff,deg);
}

// this next function is needed to multiply leading term by the rest of the polynomial.

void EasyMult (float a, int m, Polynomial p)
{
     int deg;
     float coEff;
     deg=m*p.GetDegree();
     coEff=a*p.GetCoefficient(deg);

}

If u want to talk to me right away, just IM me on AIM @ humboldtjon.  Thanks to whoever helps, i will give many points away for your generosity...
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ambienceCommented:

deg=p.GetDegree();  // what if there is no term !!!

if(deg == -1) return;  // you are missing something like that

// or perhaps

if(p.termCount() == 0) return;

coEff=p.GetCoefficient(deg);

p.DeleteTerm(deg);  // so i think that decrements the degree

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