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Sum and product of polynomials

Floryn (6)
I am new to c++, and I would greatly appreciate the help.
This is what it was given to me, and I have to do the sum and product of the polynomials.
Here is the link to all of this for better understanding: http://www.mediafire.com/?mpy78l2pvxnmg75


Consider the dense representation of polynomials
f = an*x^n +...+ a1 x + a0
as linked lists of nodes of the form
a0-> a1->...->an/
Every node is assumed to be an instance of the class
class poly {
public:
double coeff; // the value of the coefficient
poly *next; // pointer to the next element
}
Defi ne the following operations:
poly* sum(poly *f, poly *g) { ... }
which computes a dense representation of the sum of the polynomials
represented by f and g.
poly* prod(poly *f, poly *g) { ... }
which computes a dense representation of the product of polynomials rep-
resented by f and g.
Make your program interactive, to display the menu
Choose what operation to do next:
f - Read the polynomial f
g - Read the polynomial g
d - Display the values of polynomials f and g
s - Compute the polynomial sum f+g
p - Compute the polynomial product f*g
q - Quit program


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#include <iostream>

using namespace std;
#include <iostream>
#include <sstream>
#include <string>

class poly {
public:
	double coeff;
	poly *next;
	poly(double c, poly* n) : coeff(c), next(n) { }
};

/**
 * Auxiliary method that displays the program menu.
 */
char makeChoice() {
	cout << "Choose what operation to do next:" << endl <<
			"f - Read the polynomial f" << endl <<
			"g - Read the polynomial g" << endl <<
			"c - Display the coefficient of a polynomial" << endl <<
			"d - Display the values of polynomials f and g" << endl <<
			"s - Compute the polynomial sum f+g" << endl <<
			"p - Compute the polynomial product f*g" << endl <<
			"q - Quit program" << endl;
	char c;
	cin >> c;
	return c;
}

/**
 * stringPoly(poly *f) computes a string representation of polynomial h
 */
string stringPoly(poly* h) {
	stringstream convert;
	if (h == 0)
		convert << "nil";
	else {
		int deg = 0;
		while( h != 0) {
			if (deg == 0) {
				convert << h->coeff;
			} else if (h->coeff < 0) {
				convert << " " << h->coeff <<"*x^" << deg;
			} else if (h->coeff > 0) {
				convert << " +" << h->coeff << "*x^" << deg;
			}
			deg++;
			h = h->next;
		}
	}
	return convert.str();
}

/**
 * clearPoly(poly *f) clears the memory allocated to store the dense representation of f
 */
void clearPoly(poly *f) {
	if(f != 0) {
		clearPoly(f->next);
		delete f;
	}
}

/**
 * auxiliary function that computes the degree of a polynomial.
 * A null polynomial is defined to have degree -1.
 */
int degree(poly *f) {
	if (f == 0)
		return -1;
	else return 1 + degree(f->next);
}

/**
 * auxiliary function that returns the coefficient of x^d in polynomial f.
 */
int coeff(poly *f, int d) {
	int deg = degree(f);
	if (deg < d)
		return 0;
	int i = 0;
	while (i != d) {
		f = f->next;
		i++;
	}
	return f->coeff;
}
/**
 * sum(poly *f, poly *g) computes the dense representation of the polynomial f+g
 */
poly *sum(poly *f, poly *g) {
	if (f == 0) return g;
	if (g == 0) return f;
	// TODO: allocate space for the dense representation of f+g, and compute it

    return 0;
}

/**
 * prod(poly *f, *poly *g) computes the dense representation of the polynomial f*g
 */
poly *prod(poly *f, poly *g) {
	// TODO
	return 0;
}

/**
 * Reads the coefficients of a polynomial from the console
 */
poly* readPoly(string polyName) {
	cout << "Enter the sequence of coefficients a_n ... a_1 a_0"
			<< " of " << polyName << endl << "separated by spaces:" << endl << endl;
	double coeff;
	poly *f = 0;
	string str="";
	while (str=="")
		getline(cin,str);
	stringstream ss(str);
	while (ss >> coeff) {
		f = new poly(coeff,f);
	}
	return f;
}

void selectPolyAndCoeff(char &c, int &i) {
	cout << "Choose the polynomial you want to analyze (f/g): ";
	c= ' ';
	while(c!='f' && c != 'g') {
		cin >> c;
	}
	cout << "Choose the power of x whose coefficient you want to know: ";
	cin >> i;
}

int main() {
	poly *f, *g, *h;
	f = 0; g = 0;
	char answer = makeChoice();
	while (answer != 'q') {
		switch (answer) {
		case 'f':
			clearPoly(f);
			f = readPoly("f");
			break;
		case 'g':
			clearPoly(g);
			g = readPoly("g");
			break;
		case 'd':
			cout << "f=" << stringPoly(f) << endl
			<< "g=" << stringPoly(g) << endl;
			break;
		case 's':
			h = sum(f,g);
			cout << "f+g=" << stringPoly(h) << endl;
			break;
		case 'c':
			char c;
			int i;
			selectPolyAndCoeff(c,i);
			switch(c) {
			case 'f':
				cout << "Coeff. of x^"<<i<<" in f is "<< coeff(f,i) << endl;
				break;
			case 'g':
				cout << "Coeff. of x^"<<i<<" in g is "<< coeff(g,i) << endl;
				break;
			}
			break;
		case 'p':
			h = prod(f,g);
			cout << "f*g=" << stringPoly(h) << endl;
			break;
		case 'q':
			continue;
		}
		answer = makeChoice();
	}
	return 0;
}



Last edited on
rollie (304)
Please use the code tags when posting code, as reading the above is...challenging. That said, tell us a little more about what the problem is. Did you get Sum to work? How about product? In a couple test cases, what are the results you are getting vs what you were expecting?
Floryn (6)
In the line 96 I have to allocate space for the dense representation of f+g, and compute it , and in line 105 I have to allocate space for the dense representation of f*g, and compute it.
When I input the command s it returns f+g=nil, and when I input p it returns f*g=nil.
Last edited on
Floryn (6)
The link to the .pdf has all the information regarding this.
ne555 (10692)
So, ¿why you don't do that?
Floryn (6)
Because I do not know how to... I am verry, verry new to programming and well... that's about it...
mik2718 (347)
I haven't read the code but I would start from the real stuff (adding and multiplying the polys) and do the user interface stuff at the end.

I would also start with polynomial addition - this is just like adding vectors, except you must use a zero where one of the polynomials doesn't have a term.

I would also use std::list but if you have to write your own then so be it.

Once you have that working then you are on your way.
Floryn (6)
That's the thing... everything is done except for the code for sum and product of the polys, wich I don't know how to write because I am a noob at programming...
Can someone just tell me how to write the sum and product of polynomials in c++?
Floryn (6)
bump.
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