Thread: Learning C++ by Example

Originally Posted by Elysia

Where is "NewTrack" defined?

Nowhere. NewTrack is a pointer to a vector. Probably I need to add something to the print function.

Originally Posted by Elysia

Where are the functions begin, end defined?

std::vector ?
the compiler says thar are not defined, probably because the compiler don't know NewTrack is a vector type

Originally Posted by Elysia

Where are the operators ++ (prefix), != and * defined?
What the compiler say?

They are not defined

Originally Posted by Elysia

You can create a function that returns all tracks or one track, if you will. You will get less encapsulation, though, and some programmers will come to expect to be able to iterate over tracks because... it's a standard pattern for all things that are iterable (all standard contains supports it).

I think the best is return all tracks. Is it possible return all tracks an then create a functio to iterate through the tracks?

Originally Posted by Elysia

Are you really sure you are ready for this, though? I see so many beginner mistakes. I see so much confusion and problems where there really should be none. This is as simple as it gets, these last exercises.
Have you considered going through beginner books for C++ and doing all the exercises while absorbing the theory?

I want to learn.
I'm reading a book too. c++ primer 5th edition.

I know that are ways to create operators. I think this "example" is a nice way to learn, but it is messy too. There are lot of concepts to understand and learn.

Originally Posted by Elysia

Yes, but the fact that you cannot implement a simple function to print the contents of a vector is worrying that you're trying to do too much at this point in time.

I know how to print a vector.
I don't know how to access the TrackInfo vector inside Cd Class. There is something that I'm not catching.

To print the data inside TrackInfo vector I need to access the data.
I cannot create a simple accessor like:

Code:

const XTrackInfo GetTracks() const { return m_TrackInfo;}

So, with my current knowlegde I cannot continue the implementation.

Originally Posted by Elysia

Come on! What is the type of m_TrackInfo?

XMusicCd ...
So, I'm being a moron.

Trackinfo is an array of XTrackInfo type, however XMusicCD owns.

Originally Posted by Elysia

Yes, but that's not the point.
The point is that the return type of

Code:

const XTrackInfo GetTracks() const { return m_TrackInfo;}

does not match the actual type of m_TrackInfo.

It is a vector

Theres is an update:

Code:

#include <iostream>
#include <vector>
#include <string>

// You may not modify XTrackInfo
class XTrackInfo
{
    std::string m_TrackName;
    int m_Length;

public:
    XTrackInfo() {}

    XTrackInfo(std::string TrackName, int Length):
        m_TrackName(std::move(TrackName)),
        m_Length(Length)
    {}

    void SetTrackName(std::string TrackName) { m_TrackName = std::move(TrackName); }
    void SetTrackLength(int Length) { m_Length = Length; }
    const std::string& GetTrackName() const { return m_TrackName; }
    int GetTrackLength() const { return m_Length; }
};

class XMusicCd
{
private:
    // You may not modify these member variables
    std::string m_Author;
    std::vector<XTrackInfo> m_TrackInfo;

public:
    // You may not modify these member functions
    XMusicCd() {}
    XMusicCd(std::string Author, std::vector<XTrackInfo> Tracks):
        m_Author(std::move(Author)),
        m_TrackInfo(std::move(Tracks))
    {}

    void SetAuthor(std::string Author) { m_Author = std::move(Author); }

    const std::string& GetAuthor() const { return m_Author; }
    const std::vector<XTrackInfo> GetTracks() const { return m_TrackInfo;}

    int GetLength() const; // Left incomplete on purpose; you will implement it later


    void AddTrack(XTrackInfo NewTrack){
        //m_TrackInfo.emplace_back(NewTrack.GetTrackName(),NewTrack.GetTrackLength());

        m_TrackInfo.emplace_back(std::move(NewTrack));

    }


    // Add additional functions to this class as necessary to make it compile.
};



void PrintCdContents(const XMusicCd& Cd)
{
    // Implement this function such that it compiles
    // Also, to be explicit, you may not add any tracks to the CD in here. That is not the purpose of this function. You may also not change the signature of the function.
    // You shall specifically not modify the CD object by calling any setters.
   //Cd.

    std::cout << "Author : " << Cd.GetAuthor() << "\n";
    std::cout << "\n" << std::endl;
    std::cout << "Track Info" << std::endl;

    Cd.GetTracks();

//    for (auto it = NewTrack.begin(), end = NewTrack.end(); it != end; ++it)
//    {
//        std::cout << *it << " ";
//    }


}

int main()
{
    // You may not change this function
    XMusicCd MyCd;
    MyCd.SetAuthor("Hello World");
    MyCd.AddTrack(XTrackInfo("This is a test", 100));
    MyCd.AddTrack(XTrackInfo("This is a test 2", 200));
    PrintCdContents(MyCd);
}

At this moment I don't know which is the best: Create operators in order to use iterators or simply try to print the Tracks content .
I think the best pratice is the the first one.

Originally Posted by Elysia

Creating an iterator interface is the best practice. In this case, it is not that difficult, but you have to understand what iterators are and how they work first and then figure out how to make the class iterable.

Ok.
I think that I need begin(), cbegin(), end() and ++ .
Do I need create another class? A template?
Or "just" add const and const iterator keywords?

Why are you trying to mess around with iterators if you can't figure out how to print the elements of the vector in the first place? Quit trying to add added complexity to the program until you understand the basics.

I really think you need to start simpler. IMO it would be better to put the vector aside for now and just create one instance of your XTrackInfo in the XMusicCd class. Populate this single instance, then print the information. Once you demonstrate that you can work with a single instance, it should be easy to convert that knowledge to working with a vector.

Try something like:

Code:

#include <iostream>
#include <string>

class Track
{
private:
   std::string name;
   int length;
public:
   Track(std::string n, int len) : name(n), length(len) { /* Blank Body */ }

};

class Cd
{
private:
   std::string name;
      Track track;
public:
   Cd(std::string author_name, std::string track_name, int length) :
      name(author_name), track(track_name, length) { /* Blank Body */ }
};

int main()
{
   Cd cd("Big Bad Mamma", "Track 1", 10);

   /* Now create a function that will print the Authors name, the track name, and the track length.
      You'll need to create member functions to access the private data of the Track class.
      These functins could be either "getters" or an overloaded stream operator<<
      your choice. */
   cd.print();


   std::cout << "Finished" << std::endl;
   return 0;
}

Jim

Also can you provide the Author, Publisher, and date of Publication of the book you are referring to?

Jim

Originally Posted by jimblumberg

Why are you trying to mess around with iterators if you can't figure out how to print the elements of the vector in the first place? Quit trying to add added complexity to the program until you understand the basics.

I really think you need to start simpler. IMO it would be better to put the vector aside for now and just create one instance of your XTrackInfo in the XMusicCd class. Populate this single instance, then print the information. Once you demonstrate that you can work with a single instance, it should be easy to convert that knowledge to working with a vector.

Try something like:

Code:

#include <iostream>
#include <string>

class Track
{
private:
   std::string name;
   int length;
public:
   Track(std::string n, int len) : name(n), length(len) { /* Blank Body */ }

};

class Cd
{
private:
   std::string name;
      Track track;
public:
   Cd(std::string author_name, std::string track_name, int length) :
      name(author_name), track(track_name, length) { /* Blank Body */ }
};

int main()
{
   Cd cd("Big Bad Mamma", "Track 1", 10);

   /* Now create a function that will print the Authors name, the track name, and the track length.
      You'll need to create member functions to access the private data of the Track class.
      These functins could be either "getters" or an overloaded stream operator<<
      your choice. */
   cd.print();


   std::cout << "Finished" << std::endl;
   return 0;
}

Jim

I appreciate your advice, however I'm too stubborn to give up at least now.
I'm trying do both things in parallel. Learn and Implemmenting.
It is clear that I'm missing something, probably I didn't find any appeal books.