C++ error: cannot convert argument 1 from 'int' to 'const [class name]

Question

I'm writing a class to add, subtract and multiply polynomials. I'm seeing the following error:

error C2664: 'Poly::Poly(const Poly &)' : cannot convert argument 1 from 'int' to 'const Poly

coming from this statement:

return p;  // in the evaluate() function

Does anyone know how to correct this?

Thanks very much in advance. -Ryan

Here's the full code:

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

class Poly
{
private:

//  int ord;                            // the order of the polynomial
//  int coeff[100];

public:

    int ord;                            // the order of the polynomial
    int coeff[100];


    int a, b, c;
    Poly();                             // constructor
    Poly addition(Poly b);              // adds 2 polynomials
    Poly subtraction(Poly b);           // subtracts 2 polynomials
    Poly multiplication(Poly b);        // multiplies 2 polynomials
    Poly evaluate(int);                 // uses Horner's method to compute and return the polynomial evaluated at x
    Poly differentiate();               // 
    void set(int, int);                 // mutator function
    int order();
    void print();                       // prints the results
};

Poly::Poly()                            // the default constructor
{
    for (int i = 0; i < 100; i++)
    {
        coeff[i] = 0;
    }
}

void Poly::set(int a, int b)            // mutator function
{
    // coeff = new Poly[b + 1];
    coeff[b] = a;
    ord = order();
}

int Poly::order()
{
    int d = 0;
    for (int i = 0; i < 100; i++)
        if (coeff[i] != 0) d = i;
        return d;
}

void print()
{
    int coeff[] = { 0 };

    for (int i = 99; i >= 0; i--)
    {
        if (coeff[i] != 0)
        {
            cout << coeff[i] << "x^" << i << " ";
        }
    }
}

Poly Poly::evaluate(int x)
{
    int p = 0;
    for (int i = ord; i >= 0; i--)
        p = coeff[i] + (x * p);
    return p;
}

Poly Poly::differentiate()
{
    if (ord == 0)
    {
        Poly t;
        t.set(0, 0);
        return t;
    }

    Poly deriv;
    deriv.ord = ord - 1;

    for (int i = 0; i < ord; i++)
        deriv.coeff[i] = (i + 1) * coeff[i + 1];
    return deriv;
}

Poly Poly::addition(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
        c.coeff[i] += a.coeff[i];
    for (int i = 0; i <= b.ord; i++)
        c.coeff[i] += b.coeff[i];

    c.ord = c.order();

    return c;
}

Poly Poly::subtraction(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
        c.coeff[i] += a.coeff[i];
    for (int i = 0; i <= b.ord; i++)
        c.coeff[i] -= b.coeff[i];

    c.ord = c.order();

    return c;
}

Poly Poly::multiplication(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
    for (int j = 0; j <= b.ord; j++)
        c.coeff[i + j] += (a.coeff[i] * b.coeff[j]);
    c.ord = c.order();
    return c;
}

int main()
{
    Poly a, b, c, d;
    a.set(7, 4);                    //  7x^4
    a.set(1, 2);                    //   x^2

    b.set(6, 3);                    //   6x^3
    b.set(-3, 2);                   //  -3x^2

    c = a.subtraction(b);           // (7x^4 + x^2) - (6x^3 - 3x^2)

    c.print();

    cout << "\n";

    d = c.differentiate().differentiate();

    d.print();

    cout << "\n";

    cout << c.evaluate(2);          // substitute x with 2
    cin.get();

    return 0;
}

Answer 1

I have changed your code to resolve build error. Please check the diff. The modified code is

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

class Poly
{
private:

//  int ord;                            // the order of the polynomial
//  int coeff[100];

public:

    int ord;                            // the order of the polynomial
    int coeff[100];


    int a, b, c;
    Poly();                             // constructor
    Poly addition(Poly b);              // adds 2 polynomials
    Poly subtraction(Poly b);           // subtracts 2 polynomials
    Poly multiplication(Poly b);        // multiplies 2 polynomials
    int evaluate(int);                 // uses Horner's method to compute and return the polynomial evaluated at x
    Poly differentiate();               // 
    void set(int, int);                 // mutator function
    int order();
    void print();                       // prints the results
};

Poly::Poly()                            // the default constructor
{
    for (int i = 0; i < 100; i++)
    {
        coeff[i] = 0;
    }
}

void Poly::set(int a, int b)            // mutator function
{
    // coeff = new Poly[b + 1];
    coeff[b] = a;
    ord = order();
}

int Poly::order()
{
    int d = 0;
    for (int i = 0; i < 100; i++)
        if (coeff[i] != 0) d = i;
        return d;
}

void Poly::print()
{
    int coeff[] = { 0 };

    for (int i = 99; i >= 0; i--)
    {
        if (coeff[i] != 0)
        {
            cout << coeff[i] << "x^" << i << " ";
        }
    }
}

int Poly::evaluate(int x)
{
    int p = 0;
    for (int i = ord; i >= 0; i--)
        p = coeff[i] + (x * p);
    return p;
}

Poly Poly::differentiate()
{
    if (ord == 0)
    {
        Poly t;
        t.set(0, 0);
        return t;
    }

    Poly deriv;
    deriv.ord = ord - 1;

    for (int i = 0; i < ord; i++)
        deriv.coeff[i] = (i + 1) * coeff[i + 1];
    return deriv;
}

Poly Poly::addition(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
        c.coeff[i] += a.coeff[i];
    for (int i = 0; i <= b.ord; i++)
        c.coeff[i] += b.coeff[i];

    c.ord = c.order();

    return c;
}

Poly Poly::subtraction(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
        c.coeff[i] += a.coeff[i];
    for (int i = 0; i <= b.ord; i++)
        c.coeff[i] -= b.coeff[i];

    c.ord = c.order();

    return c;
}

Poly Poly::multiplication(Poly b)
{
    Poly a = *this;
    Poly c;

    for (int i = 0; i <= a.ord; i++)
    for (int j = 0; j <= b.ord; j++)
        c.coeff[i + j] += (a.coeff[i] * b.coeff[j]);
    c.ord = c.order();
    return c;
}

int main()
{
    Poly a, b, c, d;
    a.set(7, 4);                    //  7x^4
    a.set(1, 2);                    //   x^2

    b.set(6, 3);                    //   6x^3
    b.set(-3, 2);                   //  -3x^2

    c = a.subtraction(b);           // (7x^4 + x^2) - (6x^3 - 3x^2)

    c.print();

    cout << "\n";

    d = c.differentiate().differentiate();

    d.print();

    cout << "\n";

    cout<<c.evaluate(2);          // substitute x with 2
    cin.get();

    return 0;
}

Answer 2

The function is returning an int, but should return a Poly.