Thread: Learning C++ by Example

Originally Posted by Elysia

I am going to agree with jimblumberg here. This project is just way too advanced for you at the moment.
I strongly suggest you do basic exercises found in beginners' books for now. Feel free to chime in (in a new thread) if you have problems with THOSE.
Learn how to work with most standard library types. How to iterate them, insert things, delete things, etc.
THEN come back to this project.

Yes, it is advanced, but I want to reach it

I read documentation, and I don't know what is missing.

When I try to print the array, the problem is always the same.
I'm not able to convert Xmusic CD type into a char, and I know that isn't suppose too.

For which I read, I thought the following instructions were able to do what I've want, however the compiler doesn't agree with me.

Code:

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;

    std::copy(Cd.GetTracks().begin(), Cd.GetTracks().end(), std::ostreambuf_iterator<char>(std::cout));
    std::copy(Cd.GetTracks().begin(), Cd.GetTracks().end(), std::ostream_iterator<char>(std::cout, " "));
    for (auto c : Cd.GetTracks()){

       std::cout << c << ' ';
   }

    //Cd.GetTracks();
}

The complete code is here:

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;

    std::copy(Cd.GetTracks().begin(), Cd.GetTracks().end(), std::ostreambuf_iterator<char>(std::cout));
 //   std::copy(Cd.GetTracks().begin(), Cd.GetTracks().end(), std::ostream_iterator<char>(std::cout, " "));
//    for (auto c : Cd.GetTracks()){

//        std::cout << c << ' ';
//    }

    //Cd.GetTracks();


}

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);
}

Yes, it is advanced, but I want to reach it

That's fine but you need to take small steps, not giant leaps. Learn the basics then things won't seem as complicated.

IMO your latest attempt is not what you should be trying. You should be iterating through the vector with for(;;) loops not using iterators. Iterators are not the answer to every programming problem and this problem can be solved easier without their use. And as I said in my last post you need to slow down, backup and learn the basics. Start with a simpler "project" like the one I introduced in my last post. Once you understand how to access a class from within a class switching to using the vector is very very simple. But until you really understand how classes interact you'll probably never really understand what is happening and your chances for success will be doubtful.

Again in this instance I don't recommend using iterators until you actually understand how to access a single instance of your Track class.


Jim

I disagree. Iterators are the common way of iterating through every standard container.

IMO the problem here is not trying to iterate through the vector but accessing elements of the "embedded" class. Until the OP knows how to access a single instance of the "Track" class from the "CD" class he'll never be able to access the elements of the vector, using any method.

And IMO it's better to first learn to access individual elements of the vector using loops without the iterators, once this concept is learned iterators become much simpler.


Jim

Originally Posted by laserlight

There is this so-called Telescope Rule: 'Thomson's Rule for First-Time Telescope Makers: "It is faster to make a four-inch mirror then a six-inch mirror than to make a six-inch mirror."'

I have no idea if the rule is genuine, but the spirit of the rule applies here: it is faster/easier to learn by doing simpler projects and then do a more complex project than it is to do the more complex project.

I agree with you, I'll slow down. I think the root of the problem is that I've studied OOD before OOP with C++. So, since I know that is conceptuably possible I want do, however I don't know basic concepts and "tricks", which come with practice on implementation.

Originally Posted by jimblumberg

IMO the problem here is not trying to iterate through the vector but accessing elements of the "embedded" class. Until the OP knows how to access a single instance of the "Track" class from the "CD" class he'll never be able to access the elements of the vector, using any method.

This is what I felt.

I've started learning c++ a couple months. And first books and examples that I look into didn't mentioned STL, however with Elysia help and digging on another books I found out how powerfull it is.

And my current problem it is : I don't know how to acess the content of the TrackInfo inside of CD class. This is a composition problem

Originally Posted by Elysia

Sure, but you have to learn how to iterate containers anyway, even to access a single element, be that by iterators or indices, so that point is rather moot IMO. You can access individual elements of a vector with iterators, too.

I Agree, but I have a prior problem: Don't know how to access the TrackInfo Vector inside CD class.
I'm digging