Here is my code
#include <iostream>
using namespace std;
#include "mykouti.h"
int main()
{
    Kouti koutiA(2.0, 3.2, 6.0);
    Kouti koutiB(2.5, 4.0, 5.0);
    Kouti koutiC;
    // Display the volume of each box
    cout << "KoutiA volume is: " << koutiA.calculateOgkos()
        << "\nKoutiB volume is: " << koutiB.calculateOgkos()
        << endl;
    koutiC = koutiA + koutiB;
    cout << "KoutiC volume is: " << koutiC.calculateOgkos() << endl;
    return 0;
}
// mykouti.cpp
#include <iostream>
#include "mykouti.h"
//constructor that initialize Box dimensions
Kouti::Kouti(double length, double breadth,
              double height)
{
    setDimensions(length, breadth, height);
}
void Kouti::setDimensions(double mikos, double platos, double ypsos)
{
    setMikos(mikos);
    setPlatos(platos);
    setYpsos(ypsos);
}
void setMikos(double mikos)
{
   length = mikos;
}
void setPlatos(double platos)
{
   breadth = platos;
}
void setYpsos(double ypsos)
{
   height = ypsos;
}
double Kouti::calculateOgkos() const
{
    return length*breadth*height;
}
Kouti::Kouti operator+(const Kouti& b)
{
    Kouti kouti;
    kouti.length = this->length + b.length;
    kouti.breadth = this->breadth + b.breadth;
    kouti.height = this->height + b.height;
    return kouti;
}
// mykouti.h -- Box class before operator overloading
#ifndef MYKOUTI_H_
#define MYKOUTI_H_
class Kouti
{
    public:
        //constructor that initialize Box dimensions
        explicit Kouti(double = 0.0, double = 0.0, double = 0.0);
        void setDimensions(double, double, double);
        void setMikos(double);        //setlength()
        void setPlatos(double);      //setwidth()
        void setYpsos(double);        //setheigth()
        double calculateOgkos() const;
        Kouti operator+(const Kouti& b);
    private:
        double length;
        double breadth;
        double height;
};
#endif // MYKOUTI_H_
I tried to separate the code in 3 files. working from deitel book C++ 9th edition and Stephen prata C++ Primer Plus.
When I compile code I get these errors:

Can you help me solve this? thanks
 
     
    