polynomial: problem with overloading operator =

[msalman]

Hey everyone,

I'm very new to c++ and need some help with overloading operator= for a polynomial class. Here's my relevant code:

// i can't change the method signature as it is required this way
polynomial& polynomial::operator =(const polynomial& rtSide) {
	
	this->nullify(); // a method to reset variables

	polynomial result;
        // the degree method returns the degree of the polynomial
        // set coefficient method sets coefficient of the given exponent
	for (int i = 0; i <= rtSide.degree(); i++)
		result.setCoefficient(i, rtSide.coefficients.at(i));

	return result;
}

the code in my main method

polynomial * polynomials = new polynomial[NUM_POLY]; // NUM_POLY = 5;

//initialize the polynomials 
for (int i = 0; i < NUM_POLY; i++)
	polynomials[i].nullify();
.
.
.

// the code before this builds up the polynomials based on user input from command line
int i = 1; int j = 0;
polynomials[i] = polynomials[j]; //this is not working for some reasons; the polynomials[i] remains the same as it is before but the line below works

//polynomial p = polynomials[j];

I'm new to this and can't seem to pin point the problem even after wasting more than 3 hours on this. I would really appreciate if someone can guide me to the solution, thanking in advance.

[subtercosm]

Your function is creating a polynomial and modifying that. It is not modifying the object on which it was called.

Your latter example, polynomial p = polynomials[j]; , actually calls the copy constructor to initialize p. The other plausible alternative would for a zero-argument constructor to be called to initialize p, and then for operator= to be called. But that typically would be slower, so instead the C++ guys decided that using assignment syntax to initialize a variable would call the constructor.

[msalman]

^thanks for the quick reply; I get what you're saying. Does the following code look ok because it seems to be doing the trick:

polynomial& polynomial::operator =(const polynomial& rtSide) {
	
	this->nullify();

	for (int i = 0; i <= rtSide.degree(); i++)
		this->setCoefficient(i, rtSide.coefficients.at(i));

	return *this;
}

thanks for the help

[subtercosm]

I don't know what nullify does, but it looks right.

How are you handling the zero polynomial?

[msalman]

^I'm required to simply return it as 0x^0.

btw thanks for your help, it saved me load of trouble

[StuXYZ]

Please note that the code you have is 99% wrong.

Consider

Polynominal A;
A=A;

And before you say you would never do that, be very very careful of compiler opimization, double loops that i=j (e.g. for(int i=0;i<N;i++) for(int j=0;j<N;j++) and many other places.

You should write FOR EVERY operator= (-- with a MINIMUM of a paragraph of comment if you break the rule) this:

Polynomial&
Polynomial::operator=(const Polynomial& A)
{
    if (this!=&A)
      {
          // coping stuff
      }
    return *this;
}

Additionally, since you are actually in the class I stronly suspect that you don't need the

for (int i = 0; i <= rtSide.degree(); i++)
		this->setCoefficient(i, rtSide.coefficients.at(i));

which is ugly since you use setCoefficients but access coefficient directly.

but rather just

coefficients=rtSide.coefficients;

you might need to add a little index/other parameter control etc
but it is likely to be much quicker AND much less error prone.