How to access the size of another class
 CodeGuru Home VC++ / MFC / C++ .NET / C# Visual Basic VB Forums Developer.com

# Thread: How to access the size of another class

1. Junior Member
Join Date
Mar 2011
Posts
3

## How to access the size of another class

Hello, I'm having trouble with multiple parts in my polynomial program. First of all, I can't seem to find a way to access the mySize variable from the Polynomial class, also, I'm not quite sure how to combine the liketerms, and finally if you could give me some tips for the multiplication function in Polynomial class. Any help would be appreciated.

polynomial.cpp
Code:
```#include <cassert>
using namespace std;

#include "Polynomial.h"

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

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

Monomial res;

for(int i = 0; i < mySize; i++){ // Attempting to access mySize from here and combine liketerms
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 < mySize; i++){ // Attempting to access mySize from here and combine liketerms
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--;
}

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){ // Multiplication does not work properly
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];
}*/

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

}```
polynomial.h
Code:
```#include <iostream>

#ifndef PNOM
#define PNOM

const int CAPACITY = 1024;

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

Precondition:  None
Postcondition: An empty Monomial object has been constructed..
-----------------------------------------------------------------------*/
Monomial(int c,int p) { coef = c; exp = p;};

friend Monomial operator+ (Monomial&, Monomial&);

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

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

friend class Polynomial;

int getExponent() {return exp;}

int getCoefficient() {return coef;}

/*----------------------------------------------------------------------
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 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:

friend class Monomial;

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).
----------------------------------------------------------------------*/

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

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

/***** output *****/
void display(ostream & out) const;

protected:
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```

2. Elite Member Power Poster
Join Date
Oct 2007
Location
Seattle, WA
Posts
10,895

## Re: How to access the size of another class

First of all, I can't seem to find a way to access the mySize variable from the Polynomial class
I'm not sure what your problem is, need more details.

combine the liketerms
Any two Monomials within a Polynomial should have different exponents. If you end up with more than one with the same exponent during a computation, just add their coefficients.

if you could give me some tips for the multiplication function in Polynomial class
Write down the steps for doing polynomial multiplication on paper. The programming logic will be very similar.

3. Member +
Join Date
Apr 2008
Posts
726

## Re: How to access the size of another class

mySize is only in polynomial. So how does it make sense for monomial to access mySize from a monomial?

4. Junior Member
Join Date
Mar 2011
Posts
3

## Re: How to access the size of another class

Well, for now I suppose the mySize can be ignored; however, for multiplication I implemented this piece of code but the result is not correct:

Code:
``` for (i = 0; i < p1.mySize; i++){
for (int j=0; j < p2.mySize; j++){
res.myArray[i+j] = (p1.myArray[i]*p2.myArray[j]) ;
}
}```
I tried using += but I get an error stating that 'ElementType' does not define this operator. I appreciate your help

5. Elite Member Power Poster
Join Date
Oct 2007
Location
Seattle, WA
Posts
10,895

## Re: How to access the size of another class

Well, you could define operator+= for Monomial. In fact, that's usually a more useful thing to define than operator+.

Now that I look more closely at your code, I'm wondering why you're trying to do Polynomial operations in a Monomial operator. This:
Code:
`Monomial operator+(Monomial& a, Monomial& b)`
should have no need to know anything about other Monomials, only those two that are passed.

The point of confusion may be----what to do if the two monomials have different exponents? Well, you can't handle that situation, so just throw an exception or an assertion failure or something like that. This will help make sure you never pass invalid arguments to the function.

6. Junior Member
Join Date
Mar 2011
Posts
3

## Re: How to access the size of another class

Allright, well I was able to make the multiplication function work by adding a cout inside the second for and taking out the one in the main function. Now my problem is the adding liketerms and sorting the polynomial. I understand that all I'd have to do is compare the exponents and add the coefficients, but I am unsure of where to put it and how to access the seperate terms after each operation.

7. Elite Member Power Poster
Join Date
Oct 2007
Location
Seattle, WA
Posts
10,895

## Re: How to access the size of another class

If your multiplication function is truly "working", then it shouldn't matter where you do the output....

8. ## Re: How to access the size of another class

Is this for a school assignment and you need to use the 'friend' option ? If not, stop using 'friend' all together. It's bad by design.

9. Member +
Join Date
Apr 2008
Posts
726

## Re: How to access the size of another class

Originally Posted by Skizmo
... If not, stop using 'friend' all together. It's bad by design.
sorry, that's nonsense. All non-member friend operator overloads are bad by design?

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•