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Manipulating polynomials

Kkextreme (7)
Hello,

I'm having trouble manipulating polynomials using dynamic arrays and pointers. My code compiles and outputs all of the prompts, but the answers it gives are incorrect. I thought I could get this figured out and finished but I can't seem to get it and the assignment is due in less than 4 hours from now.
Any help would be greatly appreciated. Thanks!

For this assignment, you will write a C++ class which will represent a polynomial. Then
operations will be performed on polynomials and numbers. You will write functions to add,
subtract, and multiply two polynomials or a polynomial and a number.

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  #include <cmath>
#include <iostream>
using namespace std;

class polynomial
{
public:
	friend ostream& operator<<(ostream& outfile, const polynomial&);
	friend polynomial operator+(int, const polynomial&);
	friend polynomial operator*(int, const polynomial&);
	friend polynomial operator-(int, const polynomial&);

	polynomial();
	polynomial(const polynomial&);
	polynomial(int*, int);
	~polynomial();

	polynomial operator*(const polynomial&);
	polynomial operator*(int);
	polynomial operator+(const polynomial&);
	polynomial operator+(int);
	
	void operator=(const polynomial&);
	void operator=(int);
	
	polynomial operator-();
	
	polynomial operator-(const polynomial&);
	polynomial operator-(int);

private:
	int *expr;
	int degree;
};


int main()
{
	int poly1[] = {-2,4,6};
	int poly2[] = {1,3,-5};
	int poly3[] = {3, 0, 4, 0, 5};
	
	polynomial p1(poly1, 2);
	polynomial p2(poly2, 2);
	polynomial p3(poly3, 4);
	polynomial result;


	cout << "p1 = " << p1 << endl;
	cout << "p2 = " << p2 << endl;
	cout << "p3 = " << p3 << endl << endl;

	cout << endl;
	result = p1 * p2;
	cout << "p1 * p2 = " << result << endl;

	result = p2 + p1;
	cout << "p2 + p1 = " << result << endl;

	result = p1 + p3;
	cout << "p1 + p3 = " << result << endl;

	result = p1 * p3;
	cout << "p1 * p3 = " << result << endl;

	result = p1 + 5;
	cout << "p1 + 5 = " << result << endl;

	result = p2 * 6;
	cout << "p2 * 6 = " << result << endl;

	result = 4 + p3;
	cout << "4 + p3 = " << result << endl;

	result = 3 * p1;
	cout << "3 * p1 = " << result << endl;

	result = 5 - p2;
	cout << "5 - p2 = " << result << endl;

	result = 10;
	cout << "result = 10: " << result << endl << endl;

	return 0;
}

ostream& operator<<(ostream& outfile, const polynomial& p) //display the polynomial
{
	for (int i = p.degree; i >= 0; i--)
	{
		if (i == p.degree && p.expr[i] < 0)
			outfile << "-";
		else if (i != p.degree)
		{
			if (p.expr[i] > 0)
				outfile << " + ";
			if (p.expr[i] < 0)
				outfile << " - ";
		}
		if (p.expr[i] != 0)
		{
			outfile << abs(p.expr[i]);
			if (i > 0)
				outfile << "x";
			if (i > 1)
				outfile << "^" << i;
		}
	}
	return outfile;
}

polynomial operator+(int n, const polynomial& p) //add an int to the copy
{
	polynomial temp;
	
	temp.expr = new int [p.degree];
	temp.degree = p.degree;
	
	*temp.expr = p.expr[0] + n;
	return temp;
}

polynomial operator*(int n, const polynomial& p) //multiply the copy by the int
{
	polynomial temp;
	
	temp.expr = new int [p.degree];
	temp.degree = p.degree;
	
	for (int i=0; i< p.degree; i++)
	{
	temp.expr[i] = n * p.expr[i];
	}
	return temp;
}

polynomial operator-(int n, const polynomial& p) //subtract int from copy if int is first
{
	polynomial temp;
	
	temp.expr = new int [p.degree];
	temp.degree = p.degree;
	
	*temp.expr = p.expr[0] - n;
	return temp;
}

polynomial::polynomial() //cnstrctr, set priv int degree to 0, set priv expr pointer to NULL
{ 
	degree = 0;
		
	expr = NULL;
	
}

polynomial::polynomial(const polynomial& p) //copy constructor
{
	degree = p.degree;
	expr = new int [degree];
	
	for (int i=0; i<degree; i++)
		expr[i] = p.expr[i];
}

polynomial::polynomial(int *poly_expr, int d) //cnstrctr, takes int pointer and int value.
                                              //sets degree to the int value, and the int
                                              //pointer will be a dynamic array so a deep
                                              //copy of that to expr will be done
{
	degree = d;
	
	expr = new int [degree];
	
	for (int i=0; i < degree+1; i++)
	{
	expr[i] = poly_expr[i];
	}
	
}

polynomial::~polynomial() //deallocate the array that expr is pointing to
{
	delete [] expr;
}

polynomial polynomial::operator*(const polynomial& p) //multiply poly by poly
{
	polynomial temp;
	
	if (p.degree > degree)
	{
		temp.expr = new int [p.degree];
		temp.degree = p.degree;
	}
	else
	{
		temp.expr = new int [degree];
		temp.degree = degree;
	}
	
	for (int i=0; i < degree; i++)
	{
		for (int j=0; j < temp.degree; j++)
			temp.expr[i+j] += expr[i] * p.expr[j];
	}
	return temp;
	
}

polynomial polynomial::operator*(int n) //multiply poly by int
{
	polynomial temp;
	
	temp.expr = new int [degree];
	temp.degree = degree;
	
	for (int i=0; i < degree; i++)
		{
		temp.expr[i] = expr[i] * n;
		}
	return temp;
}

polynomial polynomial::operator+(const polynomial& p) //add invoking object's poly to poly
{
	polynomial temp;
	
	if (p.degree > degree)
	{
		temp.expr = new int [p.degree];
		temp.degree = p.degree;
		
		for (int i=0; i < p.degree; i++)
	{
		temp.expr[i] = expr[i] + p.expr[i];
	}
	
	}
	else
	{
		temp.expr = new int [degree];
		temp.degree = degree;
		
		for (int i=0; i < degree; i++)
	{
		temp.expr[i] = expr[i] + p.expr[i];
	}
	
	}
	
	return temp;
	
}

polynomial polynomial::operator+(int n) //add invoking object's poly to int
{
	polynomial temp;
	
	temp.expr = new int [degree];
	temp.degree = degree;
	
	temp.expr[0] = n + expr[0];
	
	return temp;
}

void polynomial::operator=(const polynomial& p) //assignment operator to perform a copy
{
	if (this != &p)
	{
		delete [] expr;
		degree = p.degree;
		expr = new int [degree];
		
		for (int i=0; i < degree; i++)
			expr[i] = p.expr[i];
		}
}

void polynomial::operator=(int n) //polynomial of degree 0 is created with 1 coefficient
{
	*expr = n;
}

polynomial polynomial::operator-() //make the polynomial a negative
{
	polynomial temp;
	
	for (int i= 0; i < degree+1; i++)
	{
	temp.expr[i] = expr[i] * -1;
	}
	
	return temp;
}

polynomial polynomial::operator-(const polynomial& p)//subtract invoking object's polynomial
													 //from another polynomial
{
	polynomial temp;
	
	if (p.degree > degree)
	{
		temp.expr = new int [p.degree];
		temp.degree = p.degree;
		
		for (int i=0; i < p.degree; i++)
	{
		temp.expr[i] = expr[i] - p.expr[i];
	}
	
	}
	else
	{
		temp.expr = new int [degree];
		temp.degree = degree;
		
		for (int i=0; i < degree; i++)
	{
		temp.expr[i] = expr[i] - p.expr[i];
	}
	
	}
	
	return temp;

}

polynomial polynomial::operator-(int n) //subtract an invoking object's polynomial from int
{
	polynomial temp;
	
	temp.expr = new int [degree];
	temp.degree = degree;
	
	*temp.expr = n - expr[0];
	return temp;
}


This is what the output should look like:

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p1 = 6x^2 + 4x - 2
p2 = -5x^2 + 3x + 1
p3 = 5x^4 + 4x^2 + 3


p1 * p2 = -30x^4 - 2x^3 + 28x^2 - 2x - 2
p2 + p1 = 1x^2 + 7x - 1
p1 + p3 = 5x^4 + 10x^2 + 4x + 1
p1 * p3 = 30x^6 + 20x^5 + 14x^4 + 16x^3 + 10x^2 + 12x - 6
p1 + 5 = 6x^2 + 4x + 3
p2 * 6 = -30x^2 + 18x + 6
4 + p3 = 5x^4 + 4x^2 + 7
3 * p1 = 18x^2 + 12x - 6
5 - p2 = 5x^2 - 3x + 4
result = 10: 10


This is the output my code is giving:

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p1 = 6x^2 + 4x - 2
p2 = -5x^2 + 3x + 1
p3 = 5x^4 + 4x^2 + 3


p1 * p2 =  - 2x - 2
p2 + p1 =  + 7x - 1
p1 + p3 =  + 17x^3 + 10x^2 + 4x + 1
p1 * p3 =  + 33x^3 + 2x^2 + 16x - 6
p1 + 5 = 12x^2 + 7x + 3
p2 * 6 = 12x^2 + 18x + 6
4 + p3 =  + 33x^3 + 2x^2 + 16x + 7
3 * p1 =  + 12x - 6
5 - p2 =  + 12x - 4
result = 10:  + 12x + 10


Thanks again for any help.
TheIdeasMan (6817)
Hi,

Without looking at any of this, by far the easiest thing to do is use a debugger.
Decide where in your code you print the value that is wrong, use the debugger to see what the values of your variables are leading up to that point. Thus deduce what & where it went wrong.

The ones that are built into IDE's are hopefully easy to use. You can put in breakpoints and have a watchlist of variable values, and step through the code 1 line at a time.


Otherwise you could spend days staring at code or putting output statements everywhere, and still might not get it fixed.

Hope all goes well
Kkextreme (7)
Thanks for the suggestion, I'm using ubuntu and coding with geany. Does that have a debugger in it? I tried looking in the ubuntu software center and the only c++ debugger listed is something called nimiver but I don't have a clue how to use it :/
TheIdeasMan (6817)
Hi,

I haven't used Geany Is it an IDE with menus etc , or is it a text editor that is C++ aware?

Which compiler are you using, because there are cmd line debuggers such gdb which works with gcc. There is a tutorial on this site on how to use it quickly. It should already (hopefully) be installed.

Depending on your installation, you may have some dev tools already installed, if not you might just have enough time to install an IDE such QtCreator, CodeBlocks, Eclipse, or even KDevelop. Then copy all your code into it, and finally use the debugger.
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