C++ - If statement still execute when comparing doubles

Question

In this project, I am expected to created a Polynomial class. Here's is what I have for the Polynomial.cpp file:

#include <iostream>
#include "Polynomial.h"
#include <stdexcept>
#include <iomanip>
#include <cmath>
#include <string>

using namespace std;

Polynomial::Polynomial(double c[], int size){ 
    set(c,size);
}

Polynomial::Polynomial(const Polynomial &poly){
    size = poly.size;
    c = new double[size];
    for(int i=0; i<size; i++){
        c[i] = poly.c[i];
    }
}

Polynomial::~Polynomial(){
    delete [] c;
}

void Polynomial::set(double ca[], int s){
    if(s < 1){
        throw std::invalid_argument("Size must be larger or equal to 1.");
    }
    else{
        size = s;
        c = new double[size];
        for(int i=0; i<size; i++){
            c[i] = ca[i];
        }
    }
}

double* Polynomial::getPointer() const{
    return c;
}

int Polynomial::getSize() const{
    return size;
}

bool Polynomial::operator ==(const Polynomial& poly) const{
    if(size != poly.size){
        return false;
    }
    int i = 0;
    int count = 0;
    while ( i < size ) {
        if ( c[i] == poly.c[i] ) {
            count++;
        }
        i++;
    }
    if ( count != size) {
        return false;
    }
    return true;
}

Polynomial Polynomial::operator +(const Polynomial& poly) const{
    int d = fabs(size - poly.size); //absolute value of size difference
    int bigger = size; //the size of the bigger polynomial
    int smaller = poly.size; //the size of the smaller polynomial
    if ( poly.size > size) {
        bigger = poly.size;
        smaller = size;
    }
    double r[bigger];
    double s[bigger];  //new coef array for the smaller polynomial with zeros coefs added

    if ( d != 0 ) {
        if(smaller = poly.size){
            for(int i=0; i < smaller; i++){
                s[i] = poly.c[i];
            }
            for(int i=smaller; i < bigger; i++){
                s[i] = 0;
            }
            for(int i=0; i < bigger; i++){
                r[i] = c[i] + s[i];
            }
        }
        else{
            for(int i=0; i < smaller; i++){
                s[i] = c[i];
            }
            for(int i=smaller; i < bigger; i++){
                s[i] = 0;
            }
            for(int i=0; i < bigger; i++){
                r[i] = poly.c[i] + s[i];
            }
        }
    }
    else {
        for ( int i = 0; i < bigger; i++) {
            r[i] = c[i] + poly.c[i];
        }
    }

    return Polynomial(r,bigger);
}

ostream& operator<<(ostream &lhs, const Polynomial &poly){
    string plus = "+";
    bool valid = false; //check if the first term of the polynomial to be printed is valid or not, valid is true when term is non-zero

if(poly.getPointer()[poly.getSize()-1] < 0){
    if(poly.getPointer()[poly.getSize()-1] != 0){
        lhs << setprecision(1) << fixed << poly.getPointer()[poly.getSize()-1] << "x^" << poly.getSize()-1 << " ";
    }
    for(int i=poly.getSize()-2; i >= 0; i--){
        if(poly.getPointer()[i] != 0 && i != 1 && i != 0){
            if(poly.getPointer()[i] > 0){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i] << "x^" << i << " ";
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i] << "x^" << i << " ";
            }
        }
        else if(poly.getPointer()[i] != 0 && i == 1){
            if(poly.getPointer()[i] > 0){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i] << "x" << " ";
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i] << "x" << " ";
            }
        }
        else if(poly.getPointer()[i] != 0 && i == 0){
            if(poly.getPointer()[i] > 0){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i];
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i];
            }
        }
    }
}
else{
    if(poly.getPointer()[poly.getSize()-1] != 0){
        lhs << setprecision(1) << fixed << noshowpos << poly.getPointer()[poly.getSize()-1] << "x^" << poly.getSize()-1 << " ";
        valid = true;
    }
    for(int i=poly.getSize()-2; i >= 0; i--){
        if(poly.getPointer()[i] != 0 && i != 1 && i != 0){
            if(poly.getPointer()[i] > 0 && valid == true){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i] << "x^" << i << " ";
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i] << "x^" << i << " ";
                valid = true;
            }
        }
        else if(poly.getPointer()[i] != 0 && i == 1){
            if(poly.getPointer()[i] > 0 && valid == true){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i] << "x" << " ";
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i] << "x" << " ";
                valid = true;
            }
        }
        else if(poly.getPointer()[i] != 0 && i == 0){
            if(poly.getPointer()[i] > 0 && valid == true){
                lhs << setprecision(1) << fixed << plus << poly.getPointer()[i];
            }
            else{
                lhs << setprecision(1) << fixed << poly.getPointer()[i];
                valid = true;
            }
        }
    }
}
return lhs;

}

Here is my test program:

#include <iostream>
#include "Polynomial.h"
#include <iomanip>

using namespace std;

int main() {
double c[] = {0,-5,3};
double d[] = {3,0,-5,0};

Polynomial p1(c,3);
Polynomial p2(d,4);
cout << "Polynomial p1 is: " << p1 << endl;
cout << "Degree of polynomial p1 is: " << noshowpos << p1.getDegree() << endl;
cout << "Polynomial p2 is: " << p2 << endl;

Polynomial p3(p1);
cout << "Polynomial p3 now is equal to p1 after copy constructor: " << p3 << endl;

bool same = p1 == p3;
cout << "Is p1 equal to p3? " << noshowpos << same << endl;

Polynomial p4 = p1 + p2;
cout << "Polynomial p4 is the sum of p1 and p2: " << p4 << endl;

So the problem I am having is with this if statement:

if(poly.getPointer()[poly.getSize()-1] != 0){
    lhs << setprecision(1) << fixed << poly.getPointer()[poly.getSize()-1] << "x^" << poly.getSize()-1 << " ";
}

When I perform the operator+ for p4 = p1 + p2, the Polynomial array of double for p4 is [3, -5, -2, 0]. So the last value of p4[size - 1] of this array is 0. As you can see above in the if statement, when I get the poly.getPointer()[poly.getSize()-1] value, it equals to 0; however when I compare it with the zero in the if statement, it still executes even though the if statement is false (0 is not equal to 0 so it should skip this if statement). I have tried running it both on an IDE and on a Linux engine; however, the result is still the same. I am not sure if it is related to this constructor which calls the set method:

Polynomial::Polynomial(double c[], int size){ 
    set(c,size);
}

void Polynomial::set(double ca[], int s){
    if(s < 1){
        throw std::invalid_argument("Size must be larger or equal to 1.");
    }
    else{
        size = s;
        c = new double[size];
        for(int i=0; i<size; i++){
            c[i] = ca[i];
        }
    }
}

Please help. Thank you.