Problem Appending object to a Vector

[clmu]

Hello!

As most people here, i'm new to c++ (and programming).
I was currently trying to write a program differentiating polynomials, where the polynomial is handed over as a string, then converted to different classes (all is fine until this point). Next i try to save the class "term" to a vector in the class "polynopmial" - which is where something goes wrong, as the output of the polynomial always is 0.

My question: how can i correctly store each "term" in the polynomial?

in short: conversion from string to "term" works, but the program is unable to store each term to "polynomial".

as far as i can see does the problem have to be related to the x.append function.

#include <iostream>
#include <cstdlib>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

class term{
private:
	double coeff;
	int power;
public:
	void setCoeff(double x) {coeff = x;}
	void setPower(int x) {power = x;}
	double getCoeff() const {return coeff;}
	double getPower() const {return power;}
	term(double a, int b) {coeff = a, power = b;};
	term() = default;
};

struct lessThanTerm{
	inline bool operator() (const term& nr1, const term& nr2){
		return (nr1.getCoeff() > nr2.getCoeff());
	}
};

class polynomial{
private:
	vector<term> termm;
public:
	term getTerm(unsigned n) {	return termm[n];} 
	int polySize() {	return termm.size();}
	void sortPoly() {	sort(termm.rbegin(), termm.rend(), 
			lessThanTerm());}
	/*void sortPoly() {	sort(termm.rbegin(), termm.rend(), 
			[this](termm){	return };}*/
	void append(term h) {	termm.push_back(h);} 
	polynomial(term h) {	termm.push_back(h);};
	polynomial() = default;
	//void simplify
};

ostream& operator<<(ostream& o, term z){
	if(z.getPower() > 1)
		o << z.getCoeff() << "x^" << z.getPower();
	else if(z.getPower() == 1)
		o << z.getCoeff() << "x";
	else if(z.getPower() == 0)
		o << z.getCoeff();
	return o;
}

ostream& operator<<(ostream& o, polynomial z){
	//z.sortPoly();
	for(int v = 0; v <= z.polySize()-1; v+=1){ 
		o << z.getTerm(v);
		if(v < z.polySize()-1)
			cout << "+";
	}
	return o;
}

istream& operator>>(istream& in, polynomial g){ 
	string z;
	cout << "Enter a polynomial in the form \"ax^n+....+bx^0\": ";
	in >> z; 		
	
	double coeff = 0;
	int power = 0;
	string coef;
	string pwr;
	int lengthOne = z.length();
	int lengthTwo = 0;
	
	for(auto i : z){
		coef.push_back(i);
		pwr.push_back(i);
		lengthTwo+=1;
		if(i == 'x'){
			coeff = stoi(coef);
			continue;
		}
		else if(i == '^'){
			pwr.clear();
			continue;
		}	
		else if(i == '+'){
			power = stoi(pwr);
			term temp{coeff, power};
			g.append(temp);
			cout << temp << '\n'; 
			coeff = 0;
			power = 0;
			coef.clear();
			continue;
		}
		else if(lengthOne == lengthTwo){
			//cout << lengthOne << '\t' << lengthTwo << '\n';
			term temp2{coeff, 0};
			g.append(temp2);
			cout << temp2 << '\n';
		}
	/*cout << coeff << '\t' << power << '\n';
	cout << coef << '\t' << pwr << '\n';*/
	}
	return in;
}

int main()
{	
	polynomial b;
	cin >> b;
	cout << b.polySize() << '\n';
	cout << b << '\n';
		return EXIT_SUCCESS;
}

[ne555]

istream& operator>>(istream& in, polynomial &g)
pass by reference, otherwise you are modifying a copy

[Handy Andy]

Hello clmu,

As I worked with your program I finally figured out how to enter the formula.

Putting break points in the program to see what happened I found the in the overloaded function "operator >>" you enter the string and the for loop picks it apart. This works fine for the lhs of "+". "coff" and "power" are given the correct numbers, but it does not work as well for the rhs of "+". "coff" receives the correct number, but there is no "+" at the end of the formula to give "power" a correct value.

When I ended the formula input with a "+" it worked correctly. This is what I tried. I just put in numbers to see what would happen and this is the output I received:

Enter a polynomial in the form "ax^n+....+bx^0": 2x3^4+5x6^7+  // <--- Notice the ending "+".

2x^4

5x^7

2
2x^4+5x^7

I added ne555's suggestion before I figured out how to enter the formula, so I do not know if it made any difference because before that I was not entering the formula correctly.

Hope that helps,

Andy

[clmu]

Thanks a LOT, I suppose it was ne555's suggestion that was the solution - of course a reference is needed as i otherwise save the "terms" in a copy of the polynomial.....