Thread: Some simple OOP help please

Hello there,

I've been programming for a while now, in various languages. But now I've decided to do it properly and learn C++.

Here's my problem, I have a class called Linear which has public and protected attributes. And I have another class - Quadratic - which inherits from Linear.

It seems to me that Quadratic is not able to access the protected attributes from Linear. (So I think anyway). The errors I get are as follows:

C:\Users\******\C++\EquationSolver\Linear.cpp In function `int main()':
22) C:\Users\******\C++\EquationSolver\Linear.cpp `dComplex Linear::root1' is protected
58) C:\Users\******\C++\EquationSolver\Quadratic.cpp within this context
17 C:\Users\******\C++\EquationSolver\Quadratic.cpp `dComplex Quadratic::root2' is protected
59) C:\Users\******\C++\EquationSolver\Quadratic.cpp within this context
C:\Users\******\C++\EquationSolver\Makefile.win [Build Error] [Quadratic.o] Error 1

My classes are as follows:
In Linear.cpp:

Code:

#include <iostream>
#include <complex>
using namespace std;

typedef complex<double> dComplex;

class Linear {
    public:
        Linear();
        // Constructor
        ~Linear();
        // Destructor
        void setA ( float value );
        float getA();
        void setB ( float value );
        float getB();
        dComplex getRoot1();
        virtual void solve();
    protected:
        float a;
        float b;
        dComplex root1;
}; 
//
Linear::Linear(){}
//
Linear::~Linear(){}

void Linear::setA(float value) {
     a = value;
}
void Linear::setB(float value) {
     b = value;
}
float Linear::getA() {
      return a;
}
float Linear::getB() {
      return b;
}
void Linear::solve() {
     root1 = -b / a;
}
dComplex Linear::getRoot1() {
      return root1;
}

In Quadratic.cpp:

Code:

#include <complex>
#include <iostream>
#include <cmath>
#include "Linear.cpp"
using namespace std;

typedef complex<double> dComplex;

class Quadratic : public Linear{
      public:
             float getC();
             void setC(float value);
             dComplex getRoot2();
             void solve();
             float disc;
      protected:
                dComplex root2;
                float c;
};
float Quadratic::getC() {
      return c;
}
void Quadratic::setC(float value) {
     c = value;
}
dComplex Quadratic::getRoot2() {
         return root2;
}
void Quadratic::solve() {
     disc = b*b - 4*a*c;
     if(disc >= 0) {
             root1 = (-b + sqrt(disc)) / (a*2);
             root2 = (-b - sqrt(disc)) / (a*2);
     } else {
            float rePart, imPart;
            rePart = -b / (2 * a);
            imPart = sqrt((4 * a * c) - (b * b)) / (2 * a);
            root1 = (rePart, imPart);
            root2 = (rePart, -imPart);
     }
}
int main(){
    Quadratic qSolve;
    float aVal, bVal, cVal;
    cout<<"Enter value for A: ";
    cin>>aVal;
    cin.ignore();
    cout<<"Enter value for B: ";
    cin>>bVal;
    cin.ignore();
    cout<<"Enter value for C: ";
    cin>>cVal;
    cin.ignore();
    qSolve.setA(aVal);
    qSolve.setB(bVal);
    qSolve.setC(cVal);
    qSolve.solve();
    cout<<"Root1 = "<<qSolve.root1<<"\n";
    cout<<"Root2 = "<<qSolve.root2<<"\n";
    cout<<"\nPress Enter to exit...";
    cin.get();
}

Thanks for your time.

P.S. If you have any tips/criticisms for me, please let me know! I only started today.

Ah silly me! I set up the public methods and don't even use them!

I'm still getting an error though, apparently I have multiple definitions of all the methods in Linear. Do you know why this is? Is it because I'm not importing a header file instead of the whole source?

Thank you for the links by the way. Looks like a very usefull resource.

OK, thank you again. I have no idea how to set up a header file haha. I'll go look it up somewhere.

Cheers.

Ah thank you very much. A contextual example really is the best thing to learn from. My application looks much more neat and elegant now. I've even got another class inheriting from Quadratic.