title: I cannot see the error in my code
body: <p>Here is my code</p>
  
  <pre><code>#include &lt;iostream&gt;
  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 &lt;&lt; "KoutiA volume is: " &lt;&lt; koutiA.calculateOgkos()
          &lt;&lt; "\nKoutiB volume is: " &lt;&lt; koutiB.calculateOgkos()
          &lt;&lt; endl;
  
      koutiC = koutiA + koutiB;
  
      cout &lt;&lt; "KoutiC volume is: " &lt;&lt; koutiC.calculateOgkos() &lt;&lt; endl;
  
      return 0;
  }
  
  // mykouti.cpp
  #include &lt;iostream&gt;
  #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&amp; b)
  {
      Kouti kouti;
      kouti.length = this-&gt;length + b.length;
      kouti.breadth = this-&gt;breadth + b.breadth;
      kouti.height = this-&gt;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&amp; b);
  
      private:
          double length;
          double breadth;
          double height;
  };
  #endif // MYKOUTI_H_
  </code></pre>
  
  <p>I tried to separate the code in 3 files. working from deitel book C++ 9th edition and Stephen prata C++ Primer Plus.<br>
  When I compile code I get these errors:</p>
  
  <p><img src="https://i.stack.imgur.com/ZH6Hs.jpg" alt="Errors"></p>
  
  <p>Can you help me solve this? thanks</p>