Hey there, I'm having trouble creating a multiplication function for the program as I have two classes to keep in mind (Monomial and Polynomial). And if possible, a little advice on how to make my for statements in the arithmetic operators more flexible to user input such as i<PolynomialSize, which I just can't seem to find a way around it. So any help or hints would be helpful. My functions work partially, by the way. Here's what I got so far:

``````/*-- Polynomial.h ---------------------------------------------------------
Defines the monomial and polynomial classes. Polynomial is implemented
basically as a list of monomials.
---------------------------------------------------------------------------*/

#include <iostream>

#ifndef PNOM
#define PNOM

const int CAPACITY = 1024;
//typedef int ElementType;

class Monomial {
private:
float coef;
int        exp;
public:
Monomial(){};
/*----------------------------------------------------------------------
Construct a Monomial object.

Precondition:  None
Postcondition: An empty Monomial object has been constructed..
-----------------------------------------------------------------------*/
Monomial(float c,int p) { coef = c; exp = p;};
/*----------------------------------------------------------------------
Construct a Monomial object with specified coeffient and exponent.

Precondition:  None
Postcondition: A Monomial object has been constructed with the
specified coeffient and exponent.
-----------------------------------------------------------------------*/
friend Monomial operator+ (Monomial&, Monomial&);
/*----------------------------------------------------------------------

Precondition:  The monomials have the same exponent.
Postcondition: A Monomial object has been created and returned.
-----------------------------------------------------------------------*/

/*-----------------------------------------------------------------------------------------------*/
//Prototypes for the functions of the exercise #5 of the homework.

friend Monomial operator- (Monomial&, Monomial&);
/*----------------------------------------------------------------------

Precondition:  The monomials have the same exponent.
Postcondition: A Monomial object has been created and returned.
-----------------------------------------------------------------------*/

friend Monomial operator* (Monomial&, Monomial&);
/*----------------------------------------------------------------------

Precondition:  The monomials do not have to have the same exponent.
Postcondition: A Monomial object has been created and returned.
-----------------------------------------------------------------------*/

/*-----------------------------------------------------------------------------------------------*/

friend ostream & operator<< (ostream & out, const Monomial & mono);
/*----------------------------------------------------------------------

Precondition:  None.
Postcondition: The coefficient and exponent (if != 0) of the monomial are
displayed in the default output device.
-----------------------------------------------------------------------*/
};

typedef Monomial ElementType;

class Polynomial
{
public:

Polynomial();
/*----------------------------------------------------------------------
Construct a List object.

Precondition:  None
Postcondition: An empty List object has been constructed; mySize is 0.
-----------------------------------------------------------------------*/

/***** empty operation *****/
bool empty() const;
/*----------------------------------------------------------------------
Check if a list is empty.

Precondition:  None
Postcondition: true is returned if the list is empty, false if not.
-----------------------------------------------------------------------*/

/***** insert and erase *****/
void insert(ElementType item, int pos);
/*----------------------------------------------------------------------
Insert a value into the list at a given position.

Precondition:  item is the value to be inserted; there is room in
the array (mySize < CAPACITY); and the position satisfies
0 <= pos <= mySize.
Postcondition: item has been inserted into the list at the position
determined by pos (provided there is room and pos is a legal
position).
-----------------------------------------------------------------------*/

void erase(int pos);
/*----------------------------------------------------------------------
Remove a value from the list at a given position.

Precondition:  The list is not empty and the position satisfies
0 <= pos < mySize.
Postcondition: element at the position determined by pos has been
removed (provided pos is a legal position).
----------------------------------------------------------------------*/

/***** output *****/
void display(ostream & out) const;
/*----------------------------------------------------------------------
Display a list.

Precondition:  The ostream out is open.
Postcondition: The list represented by this List object has been
inserted into out.
-----------------------------------------------------------------------*/

/*-----------------------------------------------------------------------------------------------*/
//Prototypes for the functions of the exercise #5 of the homework.

friend Polynomial operator+(Polynomial &, Polynomial &);
friend Polynomial operator-(Polynomial &, Polynomial &);
friend Polynomial operator*(Polynomial &, Polynomial &);

private:
int mySize;                     // current size of list stored in myArray
ElementType myArray[CAPACITY];  // array to store the Monomials

}; //--- end of List class

//------ Prototype of output operator
ostream & operator<< (ostream & out, const Polynomial & p);

#endif``````
``````/*-- Polynomial.cpp------------------------------------------------------------

This file implements List member functions.

-------------------------------------------------------------------------*/

#include <cassert>
using namespace std;

#include "Polynomial.h"

/*----------------------------------------------------------------------
Member and friend functions for Monomial.
-----------------------------------------------------------------------*/

/*-------------------------------------------------------------------------------------------*/
//Functions for the exercise #5 of the homework.

Monomial operator+(Monomial& a, Monomial& b) {
Monomial res;

for(int i = 0; i < 4; i++){
if(a.exp == b.exp){
res.coef = a.coef + b.coef;
res.exp = a.exp;
}
else if(a.exp != b.exp){
res.coef = a.coef;
res.exp = a.exp;
}
else if(b.exp != a.exp){
res.coef = b.coef;
res.exp = b.exp;
}
}
return res;
}
Monomial operator-(Monomial& a, Monomial& b) {
Monomial res;

for(int i = 0; i < res.mySize; i++){
if(a.exp == b.exp){
res.coef = a.coef - b.coef;
res.exp = a.exp;
}
else if(a.exp != b.exp){
res.coef = a.coef;
res.exp = a.exp;
}
else if(b.exp != a.exp){
res.coef = b.coef;
res.exp = b.exp;
}
}
return res;
}

Monomial operator*(Monomial& a, Monomial& b) {
Monomial res;

res.coef = a.coef * b.coef;
res.exp    = a.exp + b.exp;

return res;
}
/*-------------------------------------------------------------------------------------------*/

ostream & operator<< (ostream & out, const Monomial & mono)
{
out << mono.coef ;
if (mono.exp > 0) out << "x^" << mono.exp;
return out;
}

/*----------------------------------------------------------------------
Member and friend functions for Polinomial.
-----------------------------------------------------------------------*/

Polynomial::Polynomial()
: mySize(0)
{}

bool Polynomial::empty() const
{
return mySize == 0;
}

void Polynomial::display(ostream & out) const
{
for (int i = mySize-1; i >= 0 ; i--) {
if (i != mySize-1) out << " + ";
out << myArray[i];
}

}

ostream & operator<< (ostream & out, const Polynomial & aList)
{
aList.display(out);
return out;
}

void Polynomial::insert(ElementType item, int pos)
{
if (mySize == CAPACITY)
{
cerr << "*** No space for list element -- terminating "
"execution ***\n";
exit(1);
}
if (pos < 0 || pos > mySize)
{
cerr << "*** Illegal location to insert -- " << pos
<< ".  List unchanged. ***\n";
return;
}

// First shift array elements right to make room for item

for(int i = mySize; i > pos; i--)
myArray[i] = myArray[i - 1];

// Now insert item at position pos and increase list size
myArray[pos] = item;
mySize++;
}

void Polynomial::erase(int pos)
{
if (mySize == 0)
{
cerr << "*** List is empty ***\n";
return;
}
if (pos < 0 || pos >= mySize)
{
cerr << "Illegal location to delete -- " << pos
<< ".  List unchanged. ***\n";
return;
}

// Shift array elements left to close the gap
for(int i = pos; i < mySize; i++)
myArray[i] = myArray[i + 1];

// Decrease list size
mySize--;
}

/*-------------------------------------------------------------------------------------------*/
//Functions for the exercise #5 of the homework.

Polynomial operator+(Polynomial &p1, Polynomial &p2){
Polynomial res;
int i = 0;

if (p1.mySize > p2.mySize){
res.mySize = p1.mySize;
}else{
res.mySize = p2.mySize;
}

for(i = 0; i < res.mySize; i++){
res.myArray[i] = p1.myArray[i] + p2.myArray[i];
}

return res;

}

Polynomial operator-(Polynomial &p1, Polynomial &p2){
Polynomial res;
int i = 0;

if (p1.mySize > p2.mySize){
res.mySize = p1.mySize;
}else{
res.mySize = p2.mySize;
}

for(i = 0; i < res.mySize; i++){
res.myArray[i] = p1.myArray[i] - p2.myArray[i];
}

return res;

}

Polynomial operator*(Polynomial &p1, Polynomial &p2){
Polynomial res;
int i = 0;

if (p1.mySize > p2.mySize){
res.mySize = p1.mySize;
}else{
res.mySize = p2.mySize;
}

for(i = 0; i < res.mySize; i++){
res.myArray[i] = p1.myArray[i] * p2.myArray[i];
}

return res;

}``````
``````//--- Program to test Polynomial class.

#include <iostream>
using namespace std;

#include "Polynomial.h"

int main()
{
float coefficient;
int exp;

Polynomial myPoly01;
Polynomial myPoly02;
Polynomial poly03;

//cout << "Please enter coefficient <ENTER> power <ENTER>" << endl;
do  {
cout << "Enter coefficient of monomial (or 0 to end):";
cin >> coefficient;
if (coefficient !=0) {
cout << "Enter exponent of monomial:";
cin >> exp;
myPoly01.insert(Monomial(coefficient,exp),0); }
} while(coefficient != 0);
cout << myPoly01 << endl;

/*---------------------------------------------------------------------------------------------*/
// Edited function main() for the functions of the exercise #5 of the homework.

cout << "\nNow create another polynomial: " << endl;
do  {
cout << "Enter coefficient of monomial (or 0 to end):";
cin >> coefficient;
if (coefficient !=0) {
cout << "Enter exponent of monomial:";
cin >> exp;
myPoly02.insert(Monomial(coefficient,exp),0); }
} while(coefficient != 0);
cout << myPoly02 << endl;

cout << "\nAdding the two polynomials: " << endl;
poly03 = myPoly01 + myPoly02;
cout << poly03 << endl;

cout << "\nSubtracting the two polynomials: " << endl;
poly03 = myPoly01 - myPoly02;
cout << poly03 << endl;

cout << "\nMultiplying the two polynomials together: " << endl;
poly03 = myPoly01 * myPoly02;
cout << poly03 << endl;

return 1;

}``````

## All 2 Replies

Fundarmentaly you have two problems , (a) that you are using the wrong algorithm, (b) that you have put the multiply operator as a friend method, and not a standard method of the class.

``````class Polynominal
{
// stuff
Polynominal operator*(const Polynomial&,const Polynominal&) const;
};``````

is a better way forward.

Then you want to consider some simple polynomials and do the multiplication e.g (x^2+3x+2)*(x^3+3x)=x^5+3x^4+5x^3+9x^2+6x You get up to degree of first * degree of second polynomial terms. Therefore you are going to need a double loop e.g. one over the first array, and one over the second array of Monomials, and then you are going to have to add up individual terms [Note: If the sum of the term goes to zero it needs to be removed!!-- e.g. (x-1)*(x+1) is x^2-1.

Allright, thanks :)

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