Issues with polynomial class c++ - c++

Question

I'm working on a polynomial class that basically does +,-,*,/, and evaluates polynomials. I keep running into bugs (specifically output is incorrect) and I think it's because of one of my operation methods (maybe addition??).
EDIT: Narrowed down problem to +() operator. It cannot add polynomials and a double.
Any help would be appreciated, please!
Polynomial Class CPP:
#include <iostream>
#include "polynomial.h"
using namespace std;
/*
=======================
Constructors
=======================
*/
Polynomial::Polynomial() //default constructor
{
for ( int i = 0; i < 20; i++ )
{
coefs[i] = 0;
}
}
Polynomial::~Polynomial() {}
void Polynomial::set(int coef, int pwr){
coefs[pwr] = coef;
pwrs = degree();
}
int Polynomial::degree()
{
int d = 0;
for ( int i = 0; i < 20; i++ )
if ( coefs[i] != 0 ) d = i;
return d;
}
/*
=======================
operator=
=======================
*/
Polynomial& Polynomial::operator= ( const Polynomial& poly )
{
if ( this == &poly ) return ( *this ) ;
else{
for (int i = 0; i < 20; i++)
coefs[i] = poly.coefs[i];
}
return ( *this );
}
/*
=======================
operator+
=======================
*/
Polynomial operator+(const Polynomial& a, const Polynomial& b )
{
Polynomial c;
for ( int i = 0; i <= a.pwrs; i++ ) c.coefs[i] += a.coefs[i];
for ( int i = 0; i <= b.pwrs; i++ ) c.coefs[i] += b.coefs[i];
c.pwrs = c.degree();
return c;
}
Polynomial operator+(const Polynomial& a, const double& d)
{
Polynomial c;
for ( int i = 0; i <= a.pwrs; i++ ){
if(i == a.pwrs) {
i=i+1;
c.coefs[i] = d;
}
c.coefs[i] += a.coefs[i];
}
c.pwrs = c.degree();
return c;
}
/*
=======================
Operator-
=======================
*/
Polynomial operator- (const Polynomial& a,const Polynomial& b )
{
//Polynomial a = *this; //a is the poly on the L.H.S
Polynomial c;
for ( int i = 0; i <= a.pwrs; i++ ) c.coefs[i] += a.coefs[i];
for ( int i = 0; i <= b.pwrs; i++ ) c.coefs[i] -= b.coefs[i];
c.pwrs = c.degree();
return c;
}
/*
=======================
Operator*
=======================
*/
Polynomial operator* (const Polynomial& a, const Polynomial& b)
{
//Polynomial a = *this; //a is the poly on the L.H.S
Polynomial c;
for ( int i = 0; i <= a.pwrs; i++ )
for ( int j = 0; j <= b.pwrs; j++ )
c.coefs[i+j] += ( a.coefs[i] * b.coefs[j] );
c.pwrs = c.degree();
return c;
}
Polynomial operator*(const Polynomial& poly1, const double& d)
{
Polynomial poly;
for(int i = 0; i < 20; i++)
poly.coefs[i] = poly1.coefs[i] * d;
poly.pwrs = poly1.pwrs;
return poly;
}
Polynomial operator*(const double& d, const Polynomial& poly1)
{
Polynomial poly;
for(int i = 0; i < 20; i++)
poly.coefs[i] = d * poly1.coefs[i];
poly.pwrs = poly1.pwrs;
return poly;
}
/*
=======================
Operator/
=======================
*/
Polynomial operator/ (const Polynomial& a, const Polynomial& b)
{
Polynomial c;
for ( int i = 0; i <= a.pwrs; i++ )
for ( int j = 0; j <= b.pwrs; j++ )
c.coefs[i+j] += ( a.coefs[i] / b.coefs[j] );
c.pwrs = c.degree();
return c;
}
ostream& operator<<(ostream& out, const Polynomial& p) {
for ( int i = 19; i >= 0; i-- ) {
if(p.pwrs > 1){
if ( p.coefs[i] != 0 ) {
cout << p.coefs[i] << "x^" << i << " ";
if(p.coefs[i-1] > 0)
cout << "+";
else if(p.coefs[i-1] < 0)
cout << "";
}
}
else if (p.pwrs == 1)
cout << p.coefs[i] << "x ";
else if(p.pwrs == 0)
cout << p.coefs[i];
}
cout << endl;
}
Main:
#include <iostream>
#include "polynomial.h"
#include "monomial.h"
using namespace std;
int main(){
Polynomial a, b, c, d, e,result;
a.set(1,3); //x^3
b.set(1,2); //x^2
c.set(6,1); //6x
d.set(0.01,10); //(1/100)x^10
e.set(2,5); //2x^5
result = 4*(a+b)*(c+1)*(d-e); // 4 * (x^3+x^2) * (6x+1) * ((1/100)x^10 - 2x^5)
}

Answer 1

You probably need to set pwrs = degree(); in operator =.
Also, as #6502 pointed out, your operator + is incorrect. You could change it like this:
Polynomial operator+(const Polynomial& a, const double& d)
{
Polynomial c;
c.coefs[0] = d;
for ( int i = 0; i <= a.pwrs; i++ ){
c.coefs[i] += a.coefs[i];
}
c.pwrs = c.degree();
return c;
}
Still inefficient, but at least it should give the correct result.

Answer 2

There is a logic problem with addition of a double. In that case you only want to add to coefs[0], not to all of them.
Why are you defining an assignment operator? Isn't the default one correct for this class?

Answer 3

Besides the problem that Henrink pointed out, assigning 0.01 to coef is meaningless. As only int is accepted here.
void Polynomial::set(int coef, int pwr){
coefs[pwr] = coef;
pwrs = degree();
}